The Doctor, Jamie, and Zoe are safely back aboard the TARDIS after their harrowing adventure in the land of fiction, outside reality. They are very glad. Everything seems all right, but the Doctor goes to the console to check. Looking on the scanner, they can see that they have not landed but are suspended in space, on the dark side of the moon.

Zoe notices a light on the moon's surface, getting brighter. It is growing larger as well, coming directly toward them! It soon becomes clear that it is a missile, heading straight for them. The Doctor works the controls frantically, but finds the landing circuit jammed. That's why they're suspended in space now. Zoe and Jamie cannot take their eyes off the scanner even while the Doctor struggles with the controls.

The missile streaks toward the little police box, exploding in space at point of contact.

However, the Doctor has managed to dematerialise at the last moment and the ship rematerialises in a field on Earth.

Jamie and Zoe take stock and find that there are no bones broken and the TARDIS seems to have survived the attack. Zoe turns her mind to the question of who would fire a missile at them, especially before they even knew who they were shooing at. The Doctor suggests - with some dread - that perhaps whoever was firing already knew that.

The next question is whether they are still in the same time zone as the people who fired at them. A look at the scanner shows them that at least their current landing site is safe - they are surrounded by a herd of cattle! The crew laughs at this until they feel a severe vibration shake the ship.

Jamie laments the ongoing difficulties with the ship and Zoe suggests getting some of the circuits repaired. The Doctor agrees. He thinks, from the looks of things, that they have landed in the twentieth century and it certainly looks like England in the summer, given the rain clouds hovering over the pasture. The Doctor suggests trying to look up their old friend Professor Travers. If this is the right time zone, he could help them. The Doctor collects the damaged visual stabiliser circuit and they all head out.

Outside, the TARDIS is now invisible in the pasture. They emerge as if from thin air. This was caused by the removal of the visual stabiliser circuit. The three travellers cross the field to the nearest road where a lorry is soon lumbering toward them. The Doctor puts out his thumb to hitch a ride. Luckily for them, the driver stops.

The driver seems to be in a great hurry and is very curt. However, he does allow them to climb in the back and he agrees to take them to London. However, they only drive a short way down the lane before the lorry stops suddenly. The Doctor, Zoe and Jamie climb out to see what is wrong.

The driver is quite nervous, saying that "company security" are on his tail. He had assumed that the Doctor and his friends were from "the community" and were trying to get out like he was. He thinks it strange that they don't know what company he's talking about and wants to know how they got into this compound.

The Doctor demurs and the driver doesn't press it. Zoe asks about "the community" and the driver tells her. The company, International Electromatix, is the largest electronics manufacturers in the world. You can hardly buy a piece of equipment these days that isn't theirs. This compound is sort of a "factory town" that they set up for living, working, and manufacturing. He stops short of saying that the people inside are actually prisoners, but it is very hard to get out once you've got in, even with the right passes. Those who join the company are treated well; those who don't join seem to just "disappear". He says that he and "his people" have been trying to trace those who disappeared, but he doesn't elaborate.

Two guards on motorcycles pass them by in the opposite direction, looking over the lorry with stern glances. Luckily, they do not stop. Once they are gone, it is safe to move on. The Doctor and his friends climb back into the lorry whilst the driver starts it up again.

They reach the guard post at the entrance and a guard scrutinises the driver's pass. After a tense moment, the lorry is waved through. All of them can breathe again.

However, once they are through, the two guards on motorbikes arrive at the gate, have a word with the guard, and then tear off in pursuit of the lorry.

Out of view of the gate, the Doctor, Jamie, and Zoe hop out of the lorry. The Doctor stops to thank the driver, but he just wants to get away from here. He shoos them all away and starts to move off. The Doctor and his friends head for the hedges along the lane and get away.

Before the lorry can move away, the motorcycles catch up to it. They want to see his pass again. The driver tries to bluff, saying the pass is in order, but the guards are gruff and insistent. They want him to come back to the compound "for questioning". He refuses to go, saying that as he is no longer on International Electromatix property, they have no jurisdiction.

One of the guards draws his gun and shows him his "jurisdiction" - several bullets in the heart. The driver's body is tossed casually from the lorry, dead.

Further down the lane, the Doctor flags down another passing car and they are given a lift to London.

Shortly they stand in front of the house that the telephone directory indicated belonged to Professor Travers. Oddly, the nameplate says "Watkins". They ring the bell but receive no answer. They ring again, letting it go on until a young woman answers. She is quite cross at them for disturbing her. She says that she is trying to work. Then she disappears back into the house, leaving the door open for the others to follow her in.

It seems that the young woman is some sort of photographer. The front room is jammed with equipment and blown-up photographs. She fiddles with a camera in her hands, ignoring the visitors. She had the camera on automatic, taking pictures or herself. The mechanism has jammed and she is quite cross. The Doctor gently takes it from her and offers to help. As he works, he gets the answers he needs.

Her name is Isobel Watkins. Her uncle has let the Travers' house whilst he and his daughter are in America for a year. Turns out her uncle, Professor Watkins, is also a scientist, in applied physics formerly employed at Cavendish Lab. She is living with him because she got kicked out of her studio last week. The Doctor thinks that Professor Watkins may be able to help him with his damaged circuit. However, Isobel has no idea where he is nor does she seem to care. In fact, as soon as her camera is fixed, she's busy snapping away again. She likes Zoe's spangly catsuit quite a bit and asks her to pose.

In between snaps, Isobel says that her uncle's been away for about a week and she hasn't seen or heard from him. He is supposed to be working on some new invention but she's not really sure. She did try to get in touch with him the other day but "they" wouldn't let a call go through. "They" are International Electromatix!

This news worries the Doctor, in light of what the lorry driver told them of IE, and he presses Isobel for more information. She, however, is absorbed in shooting pictures of Zoe and just directs him to the phone. The number for IE, she says, is scribbled on the wall. The Doctor and Jamie go, leaving Zoe to be Isobel's personal fashion model.

The Doctor dials the phone, very worried now about Professor Watkins. He refuses to believe that the man's been kidnapped, but there is a mystery to be solved regarding IE. The phone is answered by a machine who responds to all of the Doctor's questions by reporting that the party he wishes to speak to is unavailable. The Doctor is angry at getting the electronic runaround and decides that their only choice is to go to International Electromatix and to try and speak to Watkins personally.

The Doctor tries to get Zoe to come with them, but she is having too much fun posing for Isobel, kitted out in a feather boa. It is rare for Isobel to have a live model (other than herself) and she doesn't want Zoe to go. She directs the Doctor back to the wall where she's scribbled the address for IE. Jamie inquires why she writes on the wall and she says it's because paper is too easy to lose!.

A short time later, the Doctor and Jamie approach the entrance to the imposing steel and glass building that houses IE's London headquarters. They enter, unaware that they are being observed by two well-dressed men in a dark car.

Inside the reception area, the Doctor finds yet another computer waiting for him. Are there any human beings working here at all? The Doctor goes through the procedure of addressing the computer. He gets the same response: party unavailable. He asks to speak to someone in authority and is told to schedule an appointment. When he tries to bypass the system to insist this is an emergency, he is brushed off as it is a "private matter" and they have no emergency status. The Doctor is frustrated and angry with the infernal machines and decides to go in search of some person in authority. They venture deeper into the building.

The two men in the car are in contact by radio with some sort of HQ. Checks are being made on the two men who just entered International Electromatix - Jamie and the Doctor. The two men in the car, very precise and efficient operatives, are on the lookout for them to leave the building.

The Doctor's movements inside the building are not unobserved. In fact, the managing director of International Electromatix, an enigmatic man called Tobias Vaughn, watches on a monitor as the Doctor and Jamie move down a corridor. Vaughn calls to his security chief, a rough-looking customer called Packer. Without the order having to be explicit, Packer knows what to do.

Meanwhile, the two men in the car outside are also under orders to find the Doctor and Jamie. HQ wants them. Top priority.

As the Doctor and Jamie round a corner, they are hit by some toxic gas issuing from hidden nozzles in the wall. Packer descends upon them as they choke and succumb, ready to strike them both. Vaughn's voice and stern gaze, issuing from a nearby communications unit, stops him cold. He doesn't want Packer interrogating them; he wants to talk to them himself.

Shortly, the two men are brought to Vaughn's office, still trying to overcome the effects of the gas. Packer wishes to be present for the questioning, just in case things get nasty, but Vaughn dismisses him sternly. In fact, Vaughn is quite pleasant when speaking to his "guests".

The Doctor recognises the false pleasantry and responds in kind. He apologises for breaking in to the building. Vaughn thinks nothing of it. He introduces himself and asks what business they have with Professor Watkins. It must be very pressing, he thinks, to make them go to the extreme of circumventing the computer receptionist. Alas, Professor Watkins is working on a very important project and refuses to be interrupted. The Doctor then wishes to drop the matter and leave, but Jamie unfortunately mentions the electronic circuits they are having difficulties with and he has no choice but to show them to Vaughn.

Vaughn looks them over keenly. The Doctor is certain he cannot suspect their origins but Vaughn checks them over carefully. Then he decides to have them sent to his experts for analysis, effectively removing them from the Doctor's possession. The Doctor cannot protest and accepts the offer of help.

The picture of cordiality, Vaughn presents Jamie with a gift - a small disposable transistor radio. It is one of IE's most popular new products. It is a small token of apology for Packer's "zealousness". Jamie accepts it gratefully, never having seen anything like it. He learns quickly how to turn it on; the Doctor shows him just as quickly how to turn it off.

Vaughn then ends the interview, saying he has a meeting to attend. Packer will show them out. There is no argument and the Doctor has lost the vital visual stabilisation circuits.

Packer shows them out with his usual bad humour, raising Jamie's ire once again. However, the Doctor has more on his mind. He noted that Vaughn was blinking far less frequently than the normal human rate of once every 10 or 15 seconds, something Jamie would never have noticed. The lad seems to accept Vaughn's charm as genuine, the Doctor does not. Underneath it all, there's something odd. Sinister. "Almost inhuman".

As if to confirm the Doctor's intuition, Vaughn turns to the blank wall at the back of his office once the strangers are gone. He activates a switch and a large section of the wall slides up and away, revealing a dark alcove.

The Doctor and Jamie leave the International Electromatix headquarters but have little time to ponder their next move. The two men who had observed them enter are waiting for them outside. The Doctor spots them immediately and changes direction. The men ease their unmarked car down the street after them.

Zoe is at last allowed to take a break from her posing and rest. She is worried about the Doctor and Jamie, who have been gone for a couple of hours now. She hopes they're all right. Isobel inquires about the circuits they would like to show to her uncle and Zoe hedges. It doesn't matter much - Isobel isn't all that interested anyway. Just making polite conversation. She's glad to have someone to talk to for a change - and to model for her. Turns out she barely makes enough money as a model for other people to afford the cameras and equipment. She can rarely afford to pay a live model and usually uses herself.

Behind the idle chatter, Isobel can sense that Zoe is still thinking about her friends. Zoe knows Jamie and the Doctor only too well - if there's trouble to be found, they'll end up in it.

Jamie and the Doctor turn down an alley along the IE building, hoping to outrun the car following them. Unfortunately, a second car arrives at the other end and blocks them in. There's nothing left to do but stop and give up. They both plop down on the sidewalk, the Doctor digging out some cards to play with. He doesn't have to wait long before the four men in dark suits are upon them.

Tobias Vaughn is meeting with his Head Research Assistant, a nerdy little man called Gregory. Gregory has been given the task of examining the odd electronic circuits from the Doctor. Unfortunately, he cannot make much of them; he's never seen anything like them. Vaughn is not pleased by this answer and sends him off to investigate further. He has one hour.

Vaughn calls up his Security Chief, Packer, and asks for photographs of the Doctor and Jamie to be taken from the security video. He wants them sent up to him at once.

Zoe and Isobel enjoy sandwiches and tea as well as a bit of music and chat. There has still been no word from the Doctor and Jamie and Zoe cannot hide her concern any longer. She's got a bad feeling about this. Isobel doesn't really understand but she's not one to shrink from a new adventure so she suggests going off after them. Zoe is pleased at this. Isobel leaves a note just in case they come back and then they're off.

The unmarked car which picked up the Doctor and Jamie takes them to an airfield just outside London. It approaches a large cargo plane sitting on the tarmac. The plane is tended to by men in uniform - soldiers. They produce a ramp into the cargo section and the car drives straight inside.

The inside of the plane is kitted out as a military HQ. Soldiers of many ranks bustle about. The two men in suits - Benton and Tracy - are clearly soldiers as well, undercover. They bring the Doctor and Jamie inside, where they are met by the C.O. To their astonishment, they know the man - Colonel Lethbridge-Stewart - whom they met in the London Underground during the invasion of the Yeti. He is now promoted to Brigadier. He is pleased to see them again after four years. To Jamie and the Doctor, it's only been a matter of months, but time is relative.

The Brigadier seems to know all about the TARDIS and to accept it. Professor Travers explained it to him after the Doctor left. After an invasion by robotic Yeti and an extraterrestrial intelligence, time travel doesn't seem that far-fetched to him! The Brigadier explains that since that event, he has been put in charge of an independent intelligence group called UNIT: United Nations Intelligence Taskforce. They investigate the unusual and unexplained. Their current mission involves International Electromatix. That's how he found them - Benton and Tracy forwarded their photographs to him and he recognised them.

The Doctor wonders what UNIT finds odd about IE. It turns out that some of the people who've gone into the IE building haven't come out again. The Brigadier wants to find out why.

Zoe and Isobel reach the IE headquarters and enter. They encounter the computer receptionist, just like the Doctor and Jamie before them. Zoe addresses it, looking for two people inquiring about Professor Watkins.

In his office, Vaughn has again activated the switch and presented himself before the alien machine. He has given the machine - and its alien controllers - images of the Doctor and Jamie. The machine, in a voice half-human, half-mechanical, says that the two men are known and recorded. They are hostile and must be destroyed. Vaughn is a bit surprised, noting that the aliens with whom he is communicating have supposedly never been on Earth before. He is told that the Doctor and Jamie are recognised from "Planet 14" and that is all.

The machine reiterates that they are to be destroyed. Their invasion plans are nearing completion and cannot be jeopardised. Vaughn promises to deal with them, although his manner betrays some annoyance with the aliens. Clearly, Vaughn is the human agent of a powerful force bent on invading Earth. However, he is not above making demands of them when he feels the need. In fact, he shows little fear of his allies at all, closing the secret door whilst the machine is still speaking.

An alarm sounds on Vaughn's desk and a monitor comes to life. The picture is that of Zoe and Isobel in the lobby, dealing with the receptionist.

Zoe is getting the same run-around that the Doctor received earlier and she is not pleased. She, like the Doctor, doesn't care much for chatty and unhelpful computers. To get back at it, she sets the machine an insoluble equation in Algol. The machine soon reacts, its circuits in complete confusion. The voice becomes slurred and the tape spools spin wildly. Smoke begins pouring from the machine as Zoe continues to input the equation. In the end, the machine explodes. Zoe and Isobel are well-pleased.

In his office, Vaughn smiles and Zoe's resourcefulness. It is the first real emotion he has displayed in some time. He calls Packer and orders the girls brought to him. His smile grows into a laugh.

Zoe sits smugly in the lobby, admiring the damage that she has caused. Isobel is also pleased with this blow against technology, but she does worry that someone might be rather annoyed with them. They decide to leave before they are caught, but it's too late. Packer and his men descend and catch them.

The Brigadier shows the Doctor and Jamie photographs of several prominent people, all of whom went into the International Electromatix building. Some didn't come out again and the ones that did were all quite "odd". Case in point is a soldier named Rutledge, a colleague of the Brigadier. He was initially cooperative regarding the UNIT investigation of Tobias Vaughn. Once he went to the place, he became obstructive. Strange.

Jamie spots a familiar face amongst the photographs - the lorry driver who picked them up outside the IE factory compound. It turns out that he is a UNIT agent, also undercover, and he has been missing for 12 hours. It clearly explains his shifty demeanour earlier but the Doctor doubts that anything bad's happened to him.

The Brigadier explains that International Electromatix controls most of the major computer lines and made a huge breakthrough in micro-monolithic circuit designs. They have practically taken over the market for both large and small electronics and their ascendance was quite sudden, almost out of nowhere. That's how UNIT got involved - the disappearance of scientists like Professor Watkins sent up flags. However, UNIT does not have the authority to actually search IE's headquarters nor can he make any public moves - Vaughn's got too many powerful people on his side.

The Doctor is still determined to find Watkins and so he and Jamie must do so himself. The Brigadier does offer him a bit of help - a small radio transceiver that is set on UNIT's frequency - and the offer of rescue should they need it. The Doctor gratefully accepts the assistance, as well as a lift back to London.

Back at Watkins' house, Jamie and the Doctor find no sign of Zoe and Isobel. There are sandwiches, however, to which they help themselves. Jamie thinks that Vaughn isn't so bad as everyone says, reminding the Doctor about the radio he gave him for no reason. The Doctor takes the radio from Jamie and turns off the noise blaring from it. However, he doesn't give it back. Instead, he starts to open the back panel much to Jamie's chagrin. Inside, he finds one of the famous micro-monolithic circuits that established IE as an electronics giant. It is neat, compact, and revolutionary. And it has nothing to do with the operation of the radio!

Jamie doesn't really understand all this and he just wants his radio back intact. Then they set about looking for a note from Zoe. They find it on the wall near the phone, along with all of Isobel's other scribblings. Thank goodness that walls can't be lost! The Doctor becomes worried when he realises that they have gone to the IE building. He and Jamie hurry out after them.

Mr. Vaughn is not wasting the charm on Zoe and Isobel as he did with the Doctor and Jamie. In fact, he is haranguing Zoe for the antics of both herself and the Doctor. Isobel sticks up for them, saying they just want to know where her uncle is. Vaughn tells her he is perfectly well but a little "uncooperative", but he thinks that now he'll be able to "persuade" him to finish his work. Thanks to her. The threat is clear, despite the calm smooth voice. Her safety will be just the push needed to keep Watkins doing as Vaughn wants him to.

Packer and his men take the startled girls into custody, promising to carry out Vaughn's order to "take care" of them.

Jamie and the Doctor decide to bypass the main entrance of the IE building, knowing that the computer receptionist won't help them. They'll have to sneak in. But before they do so, he wants to make sure they've actually gone in. He uses his tiny radio to speak to the Brigadier. He goes through the surveillance photos and finds two girls matching the descriptions of Zoe and Isobel. They are indeed inside and have not come out. The Doctor tells the Brigadier that they are going to get inside the building to search.

Captain Turner is a bit worried about these odd "amateurs" taking on Vaughn's organisation on their own, but the Brigadier knows better than to underestimate the Doctor. He's got a knack of being one jump ahead of everyone. The Brigadier is certain they'll find a way in.

Indeed they have already done so. The Doctor and Jamie investigate a railroad siding that runs alongside the IE building. It leads to a loading area at the back of the building and its gate is unlocked. They march inside.

Head Research Assistant Gregory must admit defeat concerning the circuits presented by the Doctor. The material they're made of is no known metal alloy and the electronic connections appear to be completely illogical. He can't make any sense of them. Vaughn finds this more intriguing than worrying and he wants some answers. They won't come from Gregory, who is dismissed. Vaughn instead turns to the alien machine hidden in the wall behind his desk.

Vaughn asks more questions about the Doctor, especially how his allies came to meet him on Planet 14. At first the machine refuses to answer, stating only that the Doctor is hostile and must be destroyed. Vaughn, however, is not above threats and vows to end their partnership in the conquest of Earth if he is not given the answers he requires. The machine whirrs quietly to itself before reporting that it has contacted its leaders - Vaughn will be given the answers.

Vaughn is pleased at this show of his mastery over his allies. However, the information he receives is minimal. Vaughn is told only that the Doctor has "a machine" which allows him to travel to other planets; his allies have no further information. The necessity of destroying him is reiterated and Vaughn assures his allies that he will see to that personally.

The Doctor and Jamie reach the loading area and watch from hiding as a workman carries a giant metal container with his bare hands. They believe the container is very heavy and when the workman moves off, they find that it is. He must have been some kind of superman. Very odd indeed. They hide again as the man returns, carrying another of the heavy containers with ease. Jamie and the Doctor move off, very confused but more determined than ever to find Zoe and Isobel.

An alarm sounds in Vaughn's office and Packer reports that the Doctor and Jamie are inside the building once again. Vaughn seems bemused by all of this, but he's glad to have been saved the trouble of finding the meddling Doctor himself. He wants the two of them caught, but quietly and stealthily. He suggests using Zoe and Isobel as bait to spring the trap.

Jamie and the Doctor are lost in the warehouse area, having had no luck in finding any sign of their friends. Whilst looking for some way in to the main building, they hear two screams, definitely belonging to Zoe and Isobel. They hurry back to the loading area where the screams came from.

Packer supervises as two of his guards place Zoe and Isobel, now unconscious, into the metal containers. As they are being loaded onto a waiting train, the Doctor and Jamie arrive. They see Zoe's feather boa sticking out of one of the containers and Jamie leaps into action, tackling Packer. The Doctor, knowing he's acted too rashly, grabs his companion and tries to escape into the building.

Packer continues to taunt his prisoners, seemingly hoping they'll make a move against him. It works. Jamie, incensed by their treatment of Zoe and Isobel, launches himself at the weasly Packer. However, he has anticipated and easily hurls Jamie away. Packer moves forward, his pistol raised to beat Jamie, but he is stopped when Vaughn arrives. Once again, he is sweetness and light, putting a leash on the violent Packer. But he is also clearly annoyed at the Doctor and Jamie.

The Doctor explains that they are looking for Zoe and Isobel and Vaughn does admit that they were here, but he says that they've left the building on their own. Jamie of course doesn't believe a word of this. They saw Zoe's feather boa sticking out of one of the metal containers. They know she's inside. Jamie continues his emotional assault on Vaughn until the Doctor steps in. He seems to know how to talk to the man, calm and business-like. He says it would put their minds at ease if they could look inside the containers.

Amazingly, Vaughn agrees to let them search the containers. They have been loaded onto the train returning to the factory compound. It should be just outside. Vaughn leads the two men toward the train whilst Packer lags behind. He grabs the phone and orders the train to get underway immediately. He knows full well what's inside those containers and the Doctor and the boy will not be seeing it.

Vaughn's tone is one of false sadness as he watches the train moving off. They were just a moment too late. However, Vaughn says he is going to the factory himself and offers the Doctor and Jamie a ride. The Doctor accepts, although Jamie looks dubious.

At the UNIT HQ aeroplane, the Brigadier learns from Benton of the Doctor and Jamie's venture into the IE building. Tracy followed them as far as the railway siding but couldn't go any further. They've been inside for nearly an hour. The Brigadier is concerned by their absence but becomes more worried when Benton reports that Jamie and the Doctor are coming out... escorted by Vaughn and Packer.

They are ushered into Vaughn's private car and driven off. Everything looks just fine from Benton's point of view. Even Packer seems to be behaving himself. Benton wishes to follow them but the Brigadier decides against it. He wants them tracked more discretely. Captain Turner is to board a chopper and head to the factory compound. There is no real mission, except to keep an eye on the Doctor and to be available should he call for help.

Vaughn's car makes straight for the factory compound. The guards on the gate usher them right inside. Turner's chopper hovers overhead, perhaps a bit less discretely than intended. The guards notice but they don't raise an alarm. The Brigadier urges him to back off for the moment but to stay in the area. They can't invade the compound area and must wait to see if the Doctor signals for help.

The Doctor and Jamie are escorted into the main factory building and into a lift. They are clearly not headed to inspect the railroad cars and Jamie is concerned. Vaughn tells him smoothly that the train will take some time yet to arrive. In the meantime, he'd like to ask one or two questions about the circuits the Doctor gave him. He's found them rather fascinating.

They head off toward Vaughn's office, but Vaughn and Packer lag behind. Vaughn instructs Packer to see if Professor Watkins is finished yet and says that some "encouragement" might be necessary to hurry him along. Packer smiles, knowing exactly what is meant.

Jamie and the Doctor are shown into Vaughn's office, which is an exact replica of the one in London. Only the view out of the bank of windows is different. Vaughn says it is the secret of his success: uniformity and duplication. His entire empire is built on it. Jamie and the Doctor find it downright odd.

Vaughn is again charming and pleasant. He says he's not angry, but he wants to know why the Doctor found it necessary to flout his security systems twice, and why his friend Zoe needed to overload the computer receptionist. The Doctor doesn't really have a chance to answer as Jamie butts in, asking about Zoe and Isobel. Vaughn sticks with the story that the girls left the HQ on their own and turns back to the Doctor to complement him on his scientific ability. He is talking again about the circuits.

The Doctor remains mum about the circuits, although he can tell that Vaughn suspects something. Vaughn appears to give in and to forget his interest in the circuits. He says that he will do his best to help the Doctor, trying to find some way to make Professor Watkins put aside his work and make time to help repair the circuits. He leaves the office for a moment to make some arrangements, leaving the circuits on the desk for the Doctor to retrieve.

Jamie tries to bring the Doctor's attention back to a more immediate problem - Zoe and Isobel. The Doctor assures him he hasn't forgotten about them, but they will get nowhere by annoying Vaughn. Jamie doesn't really care; to him Mr. Vaughn seems to be imperturbable. But the Doctor is worried about his interest in the TARDIS circuits, even though he says he doubts Vaughn could suspect their origin. Perhaps Professor Watkins can tell them what's really going on around here, if they do indeed get to meet with him.

In a laboratory on the property, Packer is in "conference" with Watkins. His means of making the man cooperate are blunt and vicious. He threatens Isobel if Watkins does not do as Vaughn orders. Watkins is a scientist, not well versed in violence. He is repulsed by Packer's mindlessly sadistic streak and he doesn't really believe Isobel is here at all. Thus he refuses to do as he has been ordered. However, when Vaughn joins them, he is forced to accept the situation.

Vaughn repeats the threat to Isobel's life, his voice calm and charming yet full of menace. There is a certain "machine" that Watkins has been working on, pieces of it litter the workbench. However, he has refused to complete it and has been held prisoner here for days. With Isobel's life at stake, his resistance crumbles and he agrees to cooperate, but he wants to see Isobel first and to make certain she is all right. Vaughn agrees to this.

There is one more thing. Vaughn tells Watkins he has visitors who have gone to great lengths to seek him out. He will allow them to see him. Watkins wonders if Vaughn is worried he might tell them "everything" but Vaughn assures him he knows nothing at all. Besides, Isobel's life still hangs in the balance. Vaughn is certain that the professor will do exactly as he is asked.

Alone in the office, the Doctor and Jamie have gone to the panoramic windows to get a better look at the IE factory compound. The Doctor has spied something incongruous and very interesting - a deep space radio communications system. What could be the reason for that?

Jamie spies something else of interest - a helicopter circling the perimeter of the compound. Perhaps it belongs to UNIT. However, their speculations are cut off when Packer arrives to escort them out.

Captain Turner radios in to UNIT HQ. Still no sign of the Doctor or Jamie. The Brigadier knows it's a long shot but decides to keep Turner there just in case. If they hear from the Doctor, he may need help fast.

The Doctor and Jamie have been allowed into Watkins' lab and are unchaperoned. The Doctor has explained how they came to look for him and Watkins remembers. Anne Travers told him about the Doctor in the past. She was once a student of his. Watkins talks of the Travers' trip to America but the Doctor isn't really listening. He paces the room nervously, his eyes taking in every piece of equipment.

In Vaughn's office, Packer learns that the Doctor has been on an alien planet somewhere in space. He finds it hard to believe, being a simple minded sort. Vaughn is hoping to find out more about the Doctor's strange circuits and the machine to which they belong. That is why he left them alone with Watkins. Vaughn activates a switch and a hidden camera comes to life, showing the Doctor on the screen.

Jamie has tired of all the small talk and tells Watkins why they came: the TARDIS circuits. Watkins heard about the TARDIS from Anne and is intrigued to learn more. The Doctor hesitates, trying to change the subject. Jamie cannot understand what the problem is until the Doctor points out a camera built into the wall and hidden amongst the electronic spares. The Doctor is out of its range and cannot be seen. He asks the professor to tell them what he is working on whilst he searches in his pockets for something with which to disable the camera.

Watkins explains that he is working on the cerebraton mentor, a new kind of teaching machine. It is revolutionary, he says, because it also induces emotional changes in the subject as well as imparting knowledge.

At last the Doctor finds what he is looking for and attaches a small magnet to the camera. In Vaughn's office, the picture and sound are lost. It is not a fault in the machinery, but a deliberate attempt at sabotage by the Doctor. Vaughn admires his resourcefulness.

Packer is surprised to learn that their alien allies know the Doctor and fear him. He is worried when Vaughn reveals he has disobeyed the order to destroy the Doctor as he wants to learn more about the TARDIS. Packer is a man who can only function by taking orders and he cannot understand Vaughn's desire to disobey an order. On top of that, it is clear that Packer has due reverence for the power of their allies whilst Vaughn believes that he is in control of them. Vaughn explodes with rage at Packer's insinuation to the contrary. He will show Packer who is in charge; the time has come to stop playing games with the Doctor!

Freed from observation, Watkins has quickly sketched out the situation for the Doctor. He fears that they are entirely at the mercy of Vaughn as long as Zoe and Isobel are held hostage. The Doctor isn't so sure, believing that with the Brigadier and his lot on their side, they might just stand a chance. The Doctor still wonders what Vaughn is up to; why he is kidnapping people and forcing them to work for him. Watkins thinks he is trying to gain control of the entire electronics industry. The Doctor fears his aim is much higher than that.

Vaughn bursts in and their conversation stops. He removes the magnet that the Doctor had attached to the camera, complementing him on his ingenuity. However, all pretence of innocence is now put aside. He admits that he does have Zoe and Isobel in his power. They are on the train and will be here shortly. Jamie angrily makes a move toward Vaughn but Packer restrains him, chiding him for his idle threats.

Vaughn himself never makes idle threats. His are genuine. He tells the Doctor that he wants his travel machine. If he does not cooperate, he will hand Zoe over to Packer to do with as he wishes. He gives them one hour to decide, and has Packer drag them both away. Vaughn leaves Watkins with the suggestion that he get on with his work.

Packer escorts the Doctor and Jamie to a lift. The Doctor begins babbling about having a fear of lifts, all the while miming instructions to Jamie. The Doctor provides a distraction, saying he's ready to tell Packer everything, and then he surprises Packer and knocks him down. He and Jamie rush into the lift and the door closes between them and Packer.

The Doctor borrows Jamie's dirk and prizes open the control panel of the lift. He grabs the handful or wires revealed and starts to yank them. He hopes to bring the lift to a sudden halt, but he knows that he might just as easily send them plummeting out of control. He yanks the wires and the panel sparks.

Packer is livid as he reports to Vaughn, vowing to tear them apart when he catches them. Vaughn calms him down, saying that he wants them in one piece. Packer receives a message that the lift has jammed between the fourth and fifth floors and speculates that the Doctor did this on purpose. Vaughn is sure of it, but doesn't know why. He might be playing for time, but it seems more likely that the Doctor has some plan.

In fact, he does. He points Jamie's attention to the trap door in the ceiling of the lift. He plans to escape into the lift shaft. The Doctor bends down so that Jamie can climb up on his shoulders. Jamie is duly impressed at his cleverness.

Packer orders his men to get the lift moving again quickly. He also orders a guard at the lift doors on every floor just in case. He seems a bit panicked, desperate to keep them from escaping. Vaughn is there to oversee the operation, still just as calm and cool as ever. It's actually the calmness that unnerves Packer the most.

Jamie emerges into the lift shaft and then helps the Doctor up. The shaft is dark and dirty and they are a long way from the top, but it is their only avenue of escape. A ladder runs up the shaft and the Doctor prepares to climb it. A sobering thought occurs to Jamie: what happens if the lift starts moving again? The Doctor tells him in no uncertain terms, they'll both be squashed!

It doesn't take long before Vaughn's engineers get the lift working again. Vaughn wants it brought to them on the sixth floor.

Jamie notes the sound in the shaft, indicating that the lift is preparing to move. Both he and the Doctor are worried what this means and start to climb faster. They are relieved when the lift moves up only a bit and then stops again. The Doctor figures they must be checking it. They'll soon figure out where they are. They must hurry.

Packer enters the lift, gun drawn. To his astonishment, it is empty. Vaughn erupts with anger and Packer is unnerved. He checks with his men and soon figures out that the Doctor and Jamie have escaped into the shaft. Vaughn is bored with all of this and decides to returns to his office. He barely suppresses his rage as he urges Packer not to fail again.

Packer sends his men to the roof, telling them to avoid the lift because the fugitives might be in the shaft. However, this gives him an idea. He will take the lift to the roof and if he happens to squash the fugitives in the process, too bad.

The Doctor and Jamie are nearly at the top of the shaft when they here the lift start moving again. Jamie is very worried but all he can do is keep climbing and hope they make it in time.

With luck, they beat the lift and emerge from the shaft onto the roof. They are tired but otherwise unharmed. The Doctor is ready to move off again, knowing that the guards will be upon them any moment, but Jamie would like to rest a moment. The Doctor indicates that they must get down from here in order to escape, adding to Jamie's worries. Spotting a fire escape ladder, the Doctor rushes over to it. Jamie follows, a grim look on his face.

Packer reports to Vaughn that Jamie and the Doctor have escaped from the roof. The fire escape was unguarded. At first Vaughn is calm but then suddenly explodes into a fury, shouting and spitting about Packer's incompetence. He wants the Doctor found immediately. No more excuses; no more failure!

Back on the ground, the Doctor and Jamie make their way to the railroad siding. There are now cars there which make useful camouflage for them as guards search nearby. An alarm sounds all over the compound and the Doctor leads Jamie into one of the railroad cars. They close the door behind them.

The car is filled with more of the metal containers like they saw in London. Perhaps this is the same train that came from London; perhaps Zoe and Isobel are in one of the containers among the other empties. They open one but find that it is not empty. It is full of some gauzy substance.

Suddenly the voices of Packer and his men reach them. They are about to start a search of all the rail cars. The Doctor and Jamie find places to hide, Jamie climbing into the container full of gauze and pulling the lid down over him.

As the guards' voices retreat away from their car, the Doctor climbs out of his container and helps Jamie from his. They are safe for the moment. Jamie wants to tell the Doctor about the moving thing inside the container but the Doctor is at first too worried about being found. Jamie finally gets his attention by telling that there's something alive in the container.

The Doctor is intrigued and they go to check the container but are stopped by more voices outside. Orders are given to move the girls from the train car in which they were held. The Doctor and Jamie run to the door and peek outside. They'll wait a moment and then follow. The container has been forgotten for now.

Packer stands before Vaughn, abject in his failure. He tries to assure his boss that it's only a matter of time, but Vaughn truly doubts that. The Doctor is far too clever for the clumsy likes of Packer to catch. Amazingly, Packer responds by blaming Vaughn. If he had obeyed the orders of their allies and killed the Doctor earlier, none of this would be happening.

Vaughn laughs at this. He tells Packer once again that he is fully in control of the invasion plan and of their allies. Despite their power, he is in charge, and he plans to remain in charge when the invasion is complete. Packer is stunned at the extent of Vaughn's confidence. Vaughn believes that he has an effective weapon against their allies: Professor Watkins' cerebraton machine. Their allies find the machine quite disturbing and he believes it is because of the emotions that it can generate. He is certain that emotion can be used to destroy the aliens. It is a gamble, he admits, but they are playing for high stakes and he feels it is a reasonable gamble.

Packer is worried that their allies might turn on them for disobedience but Vaughn knows he must take the chance. Otherwise, the aliens will "convert" him to be like them - totally inhuman. He refuses to let that happen, hence the development of a weapon against them. He wishes to use their might and power to take over the world, and then he will "discard them" when he is finished with them and take over Earth himself. And even if that doesn't work, he plans to have an escape route - the TARDIS. That is why they must capture the Doctor and find his travel machine. Packer is stunned at the depth of Vaughn's intelligence.

Vaughn learns that Zoe and Isobel are being taken to the main administration building. Once they are safely locked away there, he is certain that he will be able to flush out the Doctor.

Jamie and the Doctor follow the guards as they cart the container holding Zoe and Isobel toward the main administration building. They hear Packer order them sent to the central block, 10th floor. Then the guards go inside. Jamie spots the helicopter he saw earlier, still circling the compound. He's sure it's the Brigadier's men and urges the Doctor to call them up for help. The Doctor wants to hold off. They still have to rescue Zoe and Isobel first. They head off toward the central block.

In the chopper, Captain Turner reports to the Brigadier, noting the unusual activity in the compound. Lots of guards crashing about. However, there is no sign of the Doctor and Jamie. The Brigadier orders him to pull back a bit further but to stay in the area. They'll need to move quickly if the Doctor calls for help. The Brigadier also alerts his men on the ground in case a full-scale penetration of the compound is called for.

However, this level of UNIT activity finally alerts the guards and word reaches Packer and Vaughn. They've had trouble with UNIT already and they feel it is no coincidence that the Doctor is here now. He must be working with them. Packer is a bit worried that the authorities are on to them, but Vaughn is cool and in control. He will deal with this situation.

The Doctor and Jamie reach the central block and find what they are certain is the main administration building. It will be hard to find the proper room, but they must try. The Doctor is ready to climb the nearest fire escape when the ubiquitous alarm suddenly shuts off. It is replaced by Vaughn's voice echoing round the compound. Vaughn gives the Doctor just 10 minutes to give himself up or else his friend Zoe will pay the price. Just 10 minutes.

Jamie despairs of being able to find and rescue her in that short amount of time, but the challenge only galvanises the Doctor. He is certain that they can effect a "simple" rescue operation in that amount of time and charges up the fire escape. Jamie follows.

Zoe and Isobel have been locked into a disused room in the main administration building. Both are angry at their treatment and Zoe blames herself for getting them into this mess. However, they both know they have to try and get out of here. The door is securely bolted and the room is 10 floors up. Isobel goes to the window to see if there's any other way out. To her great surprise, she sees Jamie and the Doctor climbing the fire escape. She and Zoe call out to them.

Jamie sees them first and points them out to the Doctor. That's one problem solved. However, the Doctor is worried that their shouting will draw the guards. Using hand signals, he urges them to get back away from the window.

Zoe and Isobel get the message but they cannot figure out what is going on. The Doctor and Jamie keep on going to the roof of the building. They must have some plan in mind. Zoe notes that there's a hidden camera in the room with them. They can only hope it's not in use at the moment or their escape attempt will be foiled before it begins.

The Brigadier has received a call from the Doctor. He says he's not in trouble, but he needs help. He wonders if the helicopter that's been circling the area has a rope ladder on board. The Brigadier is certain it does and the Doctor gives him directions to the main building in the central block. The Brigadier doesn't quite understand what is happening, but he knows what to do.

Meanwhile, Packer receives yet another message saying his men can't find the Doctor and Jamie. He has the whole place covered, however, and is confident that it is only a matter of time. Vaughn is confident as well. He calls out over the tannoy once again, telling the Doctor he has just five minutes left to turn himself in. Packer doesn't really believe the Doctor will give himself up but Vaughn believes the threat against Zoe is enough to force his hand.

The sound of an approaching helicopter reaches them and both men go to the window. It is the same helicopter the guards reported earlier, now approaching the centre of the factory compound. Vaughn orders Packer to stop them escaping at all costs, even shooting down the helicopter if necessary.

The helicopter hovers over the roof of the main building, just above Jamie and the Doctor. The rope ladder comes down and the Doctor extends it over the edge of the building. Jamie is horrified when he figures out what the Doctor has in mind and just who is supposed to do it! Alarms go off all over the compound and Jamie moves into action. He starts climbing down the ladder toward the 10th-floor window where Zoe and Isobel are being held.

Jamie reaches the window and signals to Zoe and Isobel to barricade the door whilst he forces the window open from outside. They do so. Shortly, Jamie has the window open and climbs inside with them. He forces the window open further and then urges the girls to climb up the ladder. Isobel cannot believe what she's being asked to do, but the thought of being left to the tender mercies of Packer urges her outward and upward.

Packer and his guards gather on the ground below the main building and fire at the helicopter. But it is too high and is partially protected by the building. They do not succeed in hitting the helicopter or the people climbing up into it.

Eventually, all four make the final climb from the roof to the chopper and climb inside just as guards emerge onto the roof and begin firing from close range. Luckily, they get away unscathed.

The Brigadier listens in to all of this over the radio, particularly concerned over all of the gunfire he can hear. At last, Captain Turner reports mission accomplished - everyone is aboard unharmed and they are headed away from the compound. The Brigadier is relieved and stands down his ground troops. No assault will be necessary.

Packer is furious with his men and with himself for his failure to capture the fugitives. He is certain Vaughn will be angry as well. However, Vaughn is calm when it comes to the possible repercussions of the UNIT actions. It is only when Packer questions him that he becomes angry. Again, it is a sudden and ferocious outburst of invective. Packer is cowed into submission.

Calm again, Vaughn orders Professor Watkins' cerebraton machine loaded into his car and prepared for a return to London. Because of Packer's failure to capture the Doctor, Vaughn has decided to move the invasion forward. They have only 24 hours to prepare for it, despite the fact that the invasion force is not yet at full strength. He feels that they have sufficient strength to get the job done. Once the invasion is begun, there will be no further need for secrecy. But first, Vaughn must deal with UNIT.

He places a call to the Ministry of Defence, reaching Major General Rutledge on priority scramble. The cloak and dagger seems excessive, but not when it becomes clear that Rutledge is firmly under the control of Tobias Vaughn. The Brigadier was right to suspect something odd going on with his old friend Rutledge. Vaughn tells Rutledge that the UNIT interference with his affairs must stop. Rutledge seems a bit distracted and confused but he says that he will deal with it. Vaughn has some sort of mental hold over him and is in complete control. Rutledge will do as he says.

Back at the UNIT HQ aeroplane, The Brigadier is holding a debriefing. He is furious that Vaughn's men shot at the helicopter and he is certain that this will be proof enough that he's up to something. He's certain with this information and the details of Professor Watkins' incarceration, he can force the Ministry to take some concrete action against International Electromatix.

The Doctor is deep in thought, not really listening to the conversation. His mind has gone back to the missile that was fired at them on the other side of the moon. He's pretty certain they are still in the same time zone and he has connected that incident with Vaughn's deep space radio communications system. Captain Turner overhears this and brings up a rash of recent UFO sightings over England, wondering if they might be relevant. The Doctor wishes to see photographs if there are any and Turner goes fetch them. The Doctor looks deeply worried.

Vaughn and Packer have come to collect Professor Watkins and his machine. Watkins still has not seen Isobel and is worried about her, especially after all the shooting he heard earlier. Vaughn tells her she is perfectly safe but will only remain so if Watkins finishes his machine - to Vaughn's specifications - in 24 hours. The threat is clear and Watkins cannot resist. He goes quietly with them back to London.

The Doctor looks over the UFO photos and learns that there have been sightings off and on for over a year. Fighter planes sent up to investigate found nothing and most of the sightings disappeared somewhere over southeast England... near IE's factory compound. That's why Turner mentioned it in the first place.

The Doctor turns to Jamie and asks him again about the movement he noticed when he was hiding in the container. Something was alive underneath the gauze but Jamie says he didn't recognise it at all. Somehow, the Doctor seems to think he should have but won't say more.

Whatever is being transported in these metal containers is shipped from the factory to the London HQ, then the containers are shipped back empty. The answer to what is inside lies in the HQ. They must go back in. Jamie is none too pleased with this plan.

Captain Turner provides a scale map of the IE London HQ, including the surrounding area. Jamie tries to talk the Doctor out of this scheme, certain that the HQ will be on alert to catch them. Despite this, the Doctor presses ahead and soon finds a new way onto the premises. To get in, though, he'll need a canoe...

Some time later, the Doctor and Jamie are paddling a canoe up a canal that leads directly into the IE premises. They are in a seldom-used section of the property and all is quiet. There is no sign of any guards. They find a place to park and climb out, entering the building.

The Doctor and Jamie find their way - following light and sound - into a dingy work room. There, men in lab coats are hard at work. One of the metal containers sits upright in a corner, opened. There is something wrapped in the gauzy, cocoon-like material within. The men attach electrodes to the cocoon and activate a strange machine. The electrodes lead from the machine to the cocoon.

A high-pitched whine starts up and gains in volume and pitch. It is the hum of power, steadily rising. The creature inside the cocoon begins to stir as the power floods through it. The Doctor and Jamie watch on in mounting horror at this modern-day Frankenstein show.

Jamie stares in horror at the Cyberman coming to life in front of him. The Doctor is less stunned, but no less worried. He had begun to suspect that the Cybermen were involved in this. As quickly and quietly as they can, they back out of the work area, headed for their canoe.

They escape without incident and paddle their way out of the International Electromatix HQ.

Inside the UNIT HQ aeroplane, Zoe, Isobel and the UNIT crew discuss the situation. There's really not much left as far as Captain Turner is concerned. If there's some criminal activity going on, it will be turned over to the police. UNIT just investigates. Isobel is a bit saddened by this. She would relish the chance to jump in with some pictures of aliens or at least some military action. Now she has nothing. However, Captain Turner offers to take her to dinner to make up for her disappointment. He clearly fancies her and she him. She accepts the date.

Their conversation is interrupted when the Doctor and Jamie burst in with news of the Cybermen. Zoe is horrified but the others are just mystified. The Doctor calls the Cybermen inhuman killers from another world. Isobel thinks he's joking but the grim look on his face changes her mind quickly. The UFO's that have been spotted over the IE factory compound have been ferrying Cybermen to Earth from deep space, using Vaughn's transmitter complex to home in on. There's now an army of thousands here on Earth. Clearly the Cybermen are launching an invasion of Earth, assisted by Tobias Vaughn. One question that remains is where the army of active Cybermen are being hidden.

The Doctor learns that the Brigadier has gone to the Ministry of Defence in order to get some action taken against IE. He asks Captain Turner about the people who went into IE and came out "different". He believes that they have been mentally controlled by the Cybermen and that could spell trouble. One of the men in question is the Brigadier's immediate supervisor in the Ministry - Major General Rutlidge. Unfortunately, this is just the man he's gone to see.

As the Doctor has suspected, the Brigadier is receiving a very chilly reception from Major General Rutlidge. Despite the fact that Vaughn's guards shot at a UNIT helicopter, he refuses to see any cause for alarm and refuses all of the Brigadier's requests for action. Not even a formal investigation. The Brigadier is livid and continues to challenge his old friend Rutlidge.

As the assault continues, Rutlidge seems to falter somewhat. It is as if his resistance is actually scripted and when the Brigadier goes beyond the script, he is somewhat lost. The mental conditioning of the Cybermen. Rutlidge tries to get the Brigadier to leave the matter with him but this is not to be. The Brigadier is a man of action and he knows when action is warranted. He even goes so far as to suggest that Vaughn has some sort of hold over Rutlidge. He doesn't know how right he is.

Rutlidge forbids UNIT to take any precipitous action against International Electromatix, but the Brigadier vows to contact UNIT Central Command in Geneva to try and override him before storming out.

As soon as he is gone, Rutlidge contacts Vaughn on priority scramble. He warns Vaughn that he will not be able to hold off a UNIT investigation for long. If the Brigadier convinces central command of a problem, there will be nothing he or the Ministry can do. Vaughn takes this news calmly, certain his accelerated invasion plan will be in operation long before UNIT can act, but he wants to make sure. He asks Rutlidge how long it will take for UNIT to get the clearance they need but Rutlidge is unable to answer. He seems to be reacting against the conditioning imposed on his mind. His words stumble and he is confused.

Vaughn raises his voice and asserts his command over Rutlidge. This seems to do the trick and Rutlidge obeys his order to leave the office and come to IE headquarters immediately. Packer is worried at this evidence of a lapse in conditioning. He worries that without his assistance, the invasion plan will be compromised. Vaughn betrays no sign of worry. He is certain the conditioning will hold long enough for Rutlidge to come here to them.

Sergeant Walters, Captain Turner, and the others learn from Major General Rutlidge's secretary that he has left his office, shortly after the Brigadier did. The Brigadier must be nearly back to HQ by now. The Doctor is worried about the sudden disappearance of Rutlidge. Has the Brigadier's attempt to get his help alerted Vaughn of their concerns?

Rutlidge stands before Vaughn, blank-eyed and silent. Vaughn is still trying to determine how long it will be before the UNIT forces can act. He must bellow the question directly at the General to get a response - one or two days. He falls silent again, as if the effort of resisting the Cyberman mind control is too much for him. He's almost shut down.

Vaughn is relieved. There is time enough to complete the invasion plan if it is moved forward. Packer is still worried that UNIT may move more quickly than Rutlidge thinks. Vaughn dismisses him but decides that a little prudence is wise. He orders Packer to bring Professor Watkins' teaching machine - now complete - down to the warehouse for a little test.

Vaughn then turns to the Cyberman communications unit hidden behind his office wall. He lies and says there have been some "difficulties" and the invasion must be moved forward. It must commence at dawn tomorrow - just 15 hours from now - despite the fact that the invasion force is not yet complete. The machine reports that the Cybermen need time to consider the data but Vaughn will not accept this. He reminds them that he is in charge here on Earth. They will either do as he suggests or the partnership will end.

The machine whirs to itself for a moment, transmitting data and receiving instructions from deep space. In the end, the plan is agreed. The new invasion details will be transmitted to Vaughn as soon as they are completed. Vaughn is convinced that he has demonstrated his mastery over his alien allies.

The revival of Cybermen from the containers continues in the work room. Packer oversees this effort. The technicians working there tell him they have 50 more containers to complete. They are working as fast as they can. Packer escorts two active Cybermen into a secret room which contains a passage below ground. The Cybermen are sent into the sewers of London where the army is hidden. They are sent to join their brethren to await orders for the invasion to begin.

The Brigadier has returned to the HQ aeroplane and learned from the Doctor all that he has discovered. The Doctor already has an answer for the question of where the Cyber army is being hidden: the sewers. There's a main flood release sewer running right under the IE building. It is the perfect hiding place - many of the tunnels are dry and the water wouldn't really hurt the Cybermen anyway. And the creatures can reach almost any part of the city undetected.

As easily as the Brigadier believes all this, it is clear that they will be hard-pressed to convince UNIT central command without any real proof. Captain Turner reminds him of the earlier Yeti invasion. No one believed that until they saw the Yeti with their own eyes. They'll need some evidence to get authorisation to act.

The Doctor leaves that to the Brigadier. He is more worried about what form of attack the Cybermen are going to use to take over London. He relieves Jamie of the transistor radio Mr. Vaughn gave him, an idea forming in his mind as he dismantles it again. He wonders of there is any other IE equipment about and Captain Turner points him to it. The Doctor is eager to examine it all.

Vaughn and Gregory join Packer in the work area, ready to begin their experiment with Watkins' machine. Gregory seems a bit apprehensive however, afraid that the machine won't work against the Cybermen, but Vaughn is convinced it will work. He believes that emotions are an effective weapon against the soulless Cybermen but he must be sure. If he is to "dispose" of the creatures after the invasion, he needs to test his weapon now.

Vaughn instructs the technicians to revive the next Cyberman, just enough to bring it out of its gauzy cocoon. They do so and it stands just outside of the container. Vaughn then orders Gregory to attach the machine to the creature, a task which he fears. With trembling hands, Gregory does as instructed, attaching wires around the Cyberman's neck. Then, he switches on, using the altered teaching machine to induce fear.

The Cyberman at first does not react, but when the power is increased, it begins to move jerkily as if in pain. Vaughn is fascinated by this and orders the power increased again. The Cyberman gives an electronic cry and goes berserk. It tears the wires from its neck and lurches forward toward the humans who have attacked it. Packer pulls his pistol and fires at the creature several times. The bullets bounce harmlessly off.

Packer, Vaughn, and Gregory hide behind one of the containers, the technicians already having moved off. Luckily for them, the Cyberman's mind has been truly scrambled by the attack and so it does not pursue them. Instead, it changes direction and heads for the secret room and the sewer access in the floor. It is following its comrades down below.

Gregory sees this reaction as proof positive of his warnings - the machine is not ready. But Vaughn sees only that they have damaged the Cyberman. Watkins will alter the machine, to make it even more powerful and to provide it with remote directional control. It will work, he's sure of it.

Packer reminds them of the mad Cyberman now loose in the sewers. They can't possibly leave it down there. It would kill anyone who got in its way. Vaughn is pleased with this. Anyone who would be foolish enough to go down there deserves to die!

With the Doctor immersed in his investigations, the Brigadier and the Doctor's friends cool their heels. Isobel suggests a way for the Brigadier to get proof of the Cyberman threat: photographs of them massing in the sewers. The Brigadier agrees with this and is amazed when Isobel comes up with all the technical requirements needed for shooting in the darkness of the sewers. She clearly knows her stuff when it comes to photography. However, the Brigadier staunchly refuses to let her anywhere near the mission. This is no job for a girl! It's far too dangerous. He'll get his own military photography unit on it. Isobel is furious at the sexist attitude, especially since it was her idea in the first place.

As the Brigadier leaves, Jamie joins in the anti-feminist talk. The job's too dangerous for a girl. Zoe becomes furious as well and she and Isobel decide they're going to do the job themselves anyway. Jamie is horrified but cannot stop the two determined young women. All he can do is offer to go along to help. He wants to tell the Doctor what's happening but Zoe and Isobel leave the HQ without him. He'll lose them if he doesn't follow quickly.

The Doctor, meanwhile, is up to his neck in UNIT electronics, not even sure what he's searching for. But at last he finds something interesting - the same micro monolithic circuit contained in Jamie's radio. As with the radio, it has nothing to do with the operation of the equipment. Captain Turner can't understand why it's there if it does nothing, but the Doctor assures him the circuits have a use. He's just not sure what it is yet.

Vaughn receives final invasion details from the Cybermen. One hour prior to the invasion, Cyber transmitter units will be put into orbit around Earth. They will issue a control signal which will penetrate the entire planet and every human on Earth will be subjected to Cyber control. Then the ground forces will invade, selecting suitable humans for conversion to Cybermen. Those deemed unsuitable will be destroyed.

Vaughn reacts with fury at this. It clearly has been the Cyberman plan all along but Vaughn will not agree to it. He says that the agreed plan was that Vaughn will remain in control of Earth whilst the Cybermen plunder it for needed minerals, that is all. Vaughn insists that this remain the agreement or the invasion plan will be terminated! Clearly these two "allies" are working at cross purposes on several levels.

The Cybermen insist that Vaughn be completely converted to a Cyberman in order to control Earth but he again refuses. This is an old argument between them. His body has already been converted but his mind, that will stay human. And that is final. Amazingly, the Cybermen agree to this condition and conclude their discussion.

There is no way to gauge the plans of the Cybermen from their emotionless voice, but Vaughn is certain they do not intend to honour this agreement. Little do they know that he has a way to defeat them: the cerebraton machine. Packer worries that Vaughn hasn't thought of everything. How does he know that the Cyber control signal won't affect them as well as the other humans. Vaughn reminds him of the audio rejection capsules implanted in them. They will be protected. He has overlooked nothing.

The Doctor is now certain that the micro monolithic circuits in the IE equipment are something to do with the Cyberman invasion plan, but he can't figure it out unless he can examine them in more detail. He suggests going back to Watkins' house in London to use his laboratory. Captain Turner arranges transport for him whilst the Doctor speaks to the Brigadier.

The Brigadier is still working on organising his photographic detail when the Doctor inquires about Jamie, Zoe and Isobel. Sergeant Walters reports that they took a van and headed back to London themselves a little while ago. Said they were going to "get something important" for the Brigadier. Unfortunately, the Brigadier knows exactly what he's talking about: they are planning to go down into the sewers to get photos of the Cybermen! The Doctor is horrified, as is the Brigadier. He tries to raise Benton on the radio.

Corporal Benton, now back in uniform, is actually the driver of the van taking Zoe, Jamie, and Isobel into London. He doesn't understand what they are doing or the danger involved. Jamie, however, suspects the danger and tries to talk the girls out of this plan or at least into contacting the Doctor beforehand. They refuse to do so and hop out of the jeep as soon as they arrive. Jamie is forced to follow in order to keep up.

The Brigadier finally reaches Benton just as his passengers disembark. He reports his location as Shepherd's Street, very near the International Electromatix HQ, but he has not seen where his passengers went once they left the car. The Brigadier orders him to find and stop them immediately. Top priority.

The Brigadier despatches Captain Turner and another soldier to go and help immediately. The Doctor will hitch a ride back with them to Watkins' house, leaving Jamie, Zoe, and Isobel to UNIT's capable hands.

Jamie, Zoe, and Isobel descend into an open manhole on the street. Isobel is the last down and she is spotted by a patrolling policeman. Thinking it some sort of prank, he races over to try and get them out, shouting down the manhole.

Down in the darkness of the tunnel, Jamie is very worried about the noise. He's certain they'll have every Cyberman in the area on top of them in no time. In fact, Zoe thinks she sees something moving in the distance already. This pleases Isobel and she prepares her camera and starts snapping. Jamie is still worried as the policeman carries on shouting. Jamie thinks discretion is called for and tries to usher the girls back up the ladder, but they move off down the tunnel. Jamie is forced to follow.

The policeman climbs down the ladder, determined to find and book these three hooligans. At the bottom, he calls out for them. Suddenly he hears a noise behind him and there is the horrific sight of a Cyberman, almost on top of him. The Cyberman activates its chest unit and a burst of energy flashes from its helmet, engulfing the policeman. He collapses dead on the grimy floor of the tunnel.

Zoe and the others turn to see this, also horrified. They start to move forward away from the ladder when they realise that Zoe did indeed see something moving down there. Another Cyberman! They can't go back to the ladder because there's a Cyberman there too. They are trapped.

Jamie, Zoe, and Isobel stare in horror as they now face three Cybermen, two on one side of them and one lurching toward them, acting rather oddly.

Captain Turner, Sergeant Walters, and a private join Corporal Benton on the street above the manhole. They must hurry if they hope to rescue the young people in the sewer.

Jamie suggests they all press themselves against the tunnel wall, which they do. To their amazement, the mad Cyberman simply staggers by them, as if it cannot even see them. They cannot explain what has happened, but they are simply glad to be alive.

Turner, Walters, Benton and the private all climb down into the sewer tunnel. Captain Turner calls out for Isobel and the others. They are all armed and a bit nervous, not at all sure what they're going to find down here. Isobel wants to shout back to the captain but Jamie holds her back. There are Cybermen between them and the soldiers and he doesn't want to alert them to their presence.

Sergeant Walters worries that the young people may have been killed already, just as the policeman whose body lies on the tunnel floor. Just as they decide to go back above ground to radio the Brigadier, they see the two Cybermen just down the tunnel from them.

The Cybermen order the soldier to stand still and obey but Turner will do no such thing. Walters is armed with grenades and hands them surreptitiously to the captain. However, before he can act, the crazed Cyberman approaches the other two, flailing wildly. It crashes into the two, causing chaos to erupt in the tunnel.

Captain Turner and the others toss their grenades at the Cybermen. Two of them are down for the count, but one gets back up almost immediately. Turner is ready to unleash another barrage but the private, Perkins, cannot stand it any more. His nerve breaks and he runs for the ladder. He is quickly struck down by the same energy blast that killed the policeman.

Several more explosions rock the tunnels as the grenades do their work. As the echoes fade, Captain Turner calls out again for Isobel, Jamie, and Zoe and this time the group shouts back. The grenades have destroyed the Cybermen, or so Turner thinks, and he urges the young people to escape. They race back down the tunnel.

Turner orders everyone out, taking Perkins' body with them. He is grim as he faces Isobel and Zoe. Jamie is put on rear guard in case any of the Cybermen are still active. Turner climbs out, followed by Jamie. He is the last one out. Suddenly he cries out in pain as one of the Cybermen, still very much alive, grabs his leg in a vice-like grip. It is trying to pull him back down.

Turner grabs him and pulls against the Cyberman but he can't overcome the creature's strength. Walters hammers on the Cyberman with his rifle and Benton fetches a grenade. The battering forces the Cyberman to let go and retreat into the hole. Benton drops a grenade down the hole where it explodes a moment later. Hopefully, this has finally destroyed the Cybermen. Walters cannot believe the pounding those creatures took and still survived. They must be nearly indestructible.

The soldiers and the young people hurry back to the safety of their jeeps.

At Travers' house, the Doctor uses Watkins' lab to examine the micro monolithic circuits. He has determined that there is some kind of alien logic at work in the circuits, but he hasn't been able to work it out yet. The young people have all been brought here as well, so that Isobel can develop her photographs. The Brigadier oversees the entire group.

With the photographs and the information he has already, the Brigadier is planning to go to Geneva in the morning to make a full report to UNIT Central Command. With luck, he should have authorisation to act in two or three days. The Doctor is horrified, certain that they don't have that much time before the invasion begins.

Isobel arrives with her photographs, very proud of the fuzzy, badly-lit shots she has produced. Despite Jamie's insistence that they are clearly Cybermen, the Brigadier is disappointed. To him, who has never seen a Cyberman, the photos look very much like fakes. Irritated, Isobel storms out. She has apparently risked her life for nothing. The Brigadier is now very much worried for the case he must try to make in Geneva.

Suddenly the Doctor sits up from his microscope, his eyes wide. He thinks he may have found the answer to the alien circuits.

Packer reports the assault in the sewers to Mr. Vaughn. He is certain it was the work of UNIT and he is worried. Vaughn is not. There is not enough time for them to act no matter what proof they've uncovered. In a few hours time, the invasion will be underway and no one can stop them. In a few hours time, all that they can see out the panoramic windows - the city of London and beyond - will belong to them.

The only point that Vaughn still has to settle is the completion of Professor Watkins' cerebraton machine in its new configuration. Packer reports that the work is done. Momentarily, Gregory arrives with Watkins and the machine. Gregory is still sceptical that the machine will work, despite the addition of directional control and more power. Vaughn is pleased.

Watkins is disheveled from lack of sleep and constant supervision. He is convinced that the cerebraton machine is now a deadly weapon but he has washed his hands of the whole thing. Whatever Vaughn is going to do with it, it has nothing to do with him...or with Isobel. He wants his niece released unharmed. Quite calmly, Vaughn reports that she is free, probably sitting comfortably at home as he has done for some time now. Watkins has been obeying Vaughn's commands for no reason at all!

While Watkins seethes with hatred for the duplicitous Vaughn, IE's director examines the cerebraton machine more closely. He wishes to test it and he chooses Watkins as the target. Vaughn dials up "fear" on the machine and activates it. Watkins crumples to the floor, engulfed in a wave of fear and panic. Vaughn smiles at the power of his machine.

Gregory leaps forward to try and stop him, fearing that Watkins will be killed but Packer holds him back. Vaughn threatens to use it on Gregory, but he knows he needs them both alive for the time being. He wants these machines mass produced as quickly as possible as a defense against the Cybermen.

Watkins agrees to do as he is ordered, but not before he's said his piece. He knows that if he refuses to do the work, he will be tortured and killed. He knows he can't stand up to that and he doesn't want to die. However, he vows that if he gets half a chance, he will destroy Vaughn and vanquish his evil from the face of the Earth.

Vaughn's reaction is one of amusement, despite the venom in Watkins' voice. Vaughn takes a pistol from Packer and Watkins is certain it will be used on him. Inexplicably, Vaughn hands the gun to Watkins! He now has the means and the opportunity to follow through on his threat. After a moment's incredulity, Watkins grabs the gun and points it at Vaughn, his hands shaking badly. But he does not fire.

Vaughn taunts the little man, accusing him of not having the courage to shoot. He still does not pull the trigger. Vaughn slaps him hard, knocking him to the floor, and goads him once again, contempt in his voice. Watkins leaps to his feet, fire in his eyes, and fires three bullets at point-blank range into Vaughn's chest.

To his overwhelming horror, the bullets have no effect. Vaughn stand there smiling evilly at him and Watkins cannot believe what he sees. He faints dead away whilst Vaughn laughs. His mind may be human, but his body has been converted to that of a Cyberman. He has strength and endurance beyond his wildest imagination and he believes himself indestructible. Tobias Vaughn combines the best of both races and soon he will use his superiority to take control of the entire world. He orders Gregory and Watkins taken away to the factory compound to work on mass producing the cerebraton machines.

Back at the house, the Doctor works on the circuits and Captain Turner sets up an R/T set whilst Jamie gets some shut-eye. The house is becoming a temporary command post. Isobel brings in some tea for the Doctor, Jamie, and Turner. The captain takes the tea and thanks Isobel. He has forgiven her for her rash actions in going down into the sewers; she couldn't have really known what she was getting into. They fall into conversation about the Cybermen, two ordinary humans involved in an impossible situation against unknown alien enemies that have proven nearly indestructible. It is almost too much for them to comprehend and it is fitting that these two should find themselves drawn together now.

The Doctor cries out in frustration over his inability to solve the mystery of the circuits, waking Jamie and startling the others. At the same time, Sergeant Walters calls in over the radio, asking for the Brigadier. He reports that Corporal Benton, still on observation at the IE headquarters, has seen two guards and another man leaving the building with Professor Watkins. Benton is following them and wants to know if he should take any action.

The Brigadier is reluctant to do anything as they have no official sanction. However, everyone argues against this, including the Doctor. His argument is most persuasive - Professor Watkins' expertise and knowledge of Vaughn's operation may be of great help in their fight against the Cybermen. The Brigadier agrees and turns the operation over to Captain Turner.

Turner is ready to leave, taking a full assault platoon with him. The Brigadier warns him that Vaughn's lot will be ready for trouble and will be playing for keeps. Secretly, both Turner and the Brigadier are glad for the chance to take some action against International Electromatix.

Some time later, as night falls, Gregory stands before Mr. Vaughn, disheveled and frightened. He is reporting to Vaughn on the disastrous UNIT raid against the IE men. There were at least 30 UNIT soldiers, he says, who came out of nowhere. They shot the two guards, took the professor and left. Vaughn is certain Gregory would have been shot himself had he not run away. The cowardly scientist hangs his head in shame.

Vaughn knows that his hopes of getting the cerebraton machine into mass production before dawn are dashed. Gregory, realising this means his usefulness is at an end, begs for a chance to do it himself. He is sure he can do it. Vaughn is not so optimistic and will not give Gregory a chance to prove himself.

Gregory is released into the sewers where he is gunned down by the waiting Cybermen.

Professor Watkins is back at his home, safe and sound, although quite a bit worse for wear. The group assembled around him is glad to have him back alive, but the Doctor is disappointed to learn that he knows nothing about the micro monolithic circuits or plans for the Cyberman invasion. However, the information on his cerebraton mentor machine is of great value. The Doctor realises that Vaughn is planning to use the machine against the Cybermen, using powerful emotional pulses to destroy them. And then suddenly it all becomes clear to the Doctor: the micro monolithic circuits are themselves emotional circuits. That's why they weren't logical. The Doctor races to the microscope and examines them again, falling into deep contemplation.

The Brigadier returns to control for his morning flight to Geneva whilst Jamie decides to take another wee nap. Zoe is disgusted by her friend's cavalier attitude to the danger they face.

In the sewers of London, the Cybermen move to their positions in preparation for the invasion. Many are now armed with metal rifle-like weapons and they mass in formation unseen by anyone, ready to strike.

Zoe wakes Jamie with urgent news. The Doctor has made a breakthrough and is giving a briefing. On a board he has drawn the Earth and the moon. Behind the moon is the Cyberman spaceship which fired the missile at the TARDIS. It is their main force and is also the start of the invasion. If the Doctor is right, the spaceship will circle around the moon to face the Earth and then use the Earth's own communications satellites to boost signals to cover the entire planet. The signals would activate the micro monolithic circuits in all IE equipment and produce the hypnotic signal that the Cybermen use to control human beings. The Earth will be in their thrall.

The Doctor tells the surprised UNIT members that there is a way to resist the Cyber signals; tiny depolarisers worn at the back of the neck will absorb the signal and protect the wearer. They were used quite successfully on the space station where he and Jamie met Zoe in the midst of a Cyber invasion. What the Doctor is not sure is how soon the signal will come and the invasion will start. He thinks it is not long. Professor Watkins has some neuristors in the house somewhere. Zoe goes with him to find them and to make the depolarisers as quickly as possible.

Dawn is starting to break over London. Vaughn gazes out of the city as the alien apparatus addresses him from its alcove. There is one hour to invasion time. The countdown begins now. Their spaceship is moving into position now, ready to transmit the Cyber signal. The Doctor was right on all counts. If he only knew....

The Doctor reports his findings to the Brigadier, en route to Geneva. He stresses the need to get his men fitted with depolarisers immediately. He will do all he can. Zoe returns with the sad news that she could only find three neuristors. It is not nearly enough to protect them. The Doctor begins urgently scouring the equipment in the laboratory. Everyone joins in, certain they have little time.

The Cybermen report to Vaughn that they are now under way. The signal will commence in 40 minutes' time. Vaughn is convinced that a few moments after that, he will be the supreme ruler of Earth. Packer is not as certain as Vaughn, his fear of the Cybermen's might still being quite healthy.

All is quiet and still at Travers' house as dawn breaks. Isobel gazes out the window, joined by Captain Turner. The two have become very comfortable with each other in the face of their shared adversity. However, Turner wonders whether the Doctor could be wrong about the impending invasion. It all seems so outlandish to him. Isobel can sympathise with his doubts. It all seems too peaceful outside to be the eve of an alien invasion.

However, the calm is suddenly shattered as a piercing sound begins issuing from everywhere, burrowing into their very brains.

The invasion has begun.

In the lab, the Doctor hears the sound too. It hits him hard and he suddenly realises that his depolariser must have fallen off. He topples to the floor as the Cyber signal attacks his brain. Zoe struggles to find a depolariser to try and save him.

The irresistible sound blankets London and the whole world. The results here are the same as everywhere - people are knocked off their feet and turned into zombies. They are all rendered unconscious almost the instant the sound hits their brains. Just as planned, the Cybermen gain control of the entire planet.

Only Vaughn's men and those fitted with neuristors by Zoe are immune to the signal. In Travers' house, Zoe and the others struggle to revive the Doctor. He is fitted with a new depolariser but still is unconscious. Chaos reigns in the laboratory.

Captain Turner enters with grim news. They've just spotted hundreds of Cybermen emerging from the sewers all around London.

As the Cybermen burst from the sewers to take over the streets of London, the Doctor's friends struggle to revive him from the effects of Cyber control. Zoe has affixed a new depolariser to his neck and he is just now coming round. He looks to be fine and his mind quickly turns to the matter at hand.

Everyone in the house has been spared the effects of the Cyber signal, but they have not yet heard from the Brigadier. Captain Turner reaches Sergeant Walters by radio. The Brigadier is fine, back on the ground after aborting his trip to Geneva. However, only half of his men have recovered so far. No final word yet on other UNIT teams around the city. Reports are still coming in.

The Brigadier thinks it would be better to get them all away from the house and he plans to send Sergeant Walters with a jeep to get them. He warns them to stay put as the streets are swarming with Cybermen. Captain Turner is afraid this means a total success for Vaughn and the Cybermen. The Doctor doesn't necessarily agree, but he does know that he and his friends are all in great danger.

In his office, Vaughn learns from the Cybermen that their full invasion force is now preparing for flight. All they need is for Vaughn to transmit the radio beam into space for them to home in on. He will do so, but first he wants an agreement from the Cybermen that all troops will remain under his control. He must work hard to overcome the Cybermen's distrust, saying that this is a necessary step as he knows the Earth and its organisation. The Cybermen do not. Unfortunately, they do not accept this argument.

Vaughn tries again with his old tactic - he refuses to transmit the homing signal unless all Cybermen on Earth are kept under his command as they are now. After a long pause for consideration, the Cybermen agree. Vaughn is playing a dangerous game with his powerful allies, certain he can win. However, neither side seems deluded as to who is double-crossing whom.

Vaughn still needs more of the cerebraton machines produced before the Cybermen arrive; he must have insurance when they eventually turn against him. He orders Packer to go to Travers' house and collect Professor Watkins. He should find no resistance as he expects all of the UNIT troops and the Doctor to be under Cyber control like the rest of the world. It should be easy.

Sergeant Walters arrives at Travers' house to transport the Doctor and the others. He has had to negotiate around hundreds of Cybermen on his way. Turner tries to rustle everyone together to leave quickly. However, they have another problem. Packer and his guards arrive outside, determined to find and take Professor Watkins.

Turner locks the door and herds everyone out the back way quickly. Jamie and Watkins are the last in the group and Watkins is hit by a bullet fired through the window. Turner fires back and then hustles the injured professor out the back door. Jamie brings up the rear and he too is shot in the leg as he retreats. Ignoring the pain, he hobbles out to join the others.

At the UNIT HQ aboard the cargo plane, the Brigadier receives an urgent message from Captain Turner. They need help fast; a chopper. Luckily, several UNIT pilots are free from Cyber control and one is actually airborne near their location. The Brigadier sends them to sector five, along with the chopper. They will rendezvous shortly.

Packer reports to a very angry Mr. Vaughn. He cannot understand how the UNIT people could escape Cyber control, although he is certain that it is something to do with the clever Doctor. Packer repeats his assertion that Vaughn should have killed the Doctor earlier when he had the chance but Vaughn is in no mood to be lectured. All hope of mass producing the cerebraton machines is ended but Vaughn decides he must go on with his plan. He must somehow take on the Cybermen using the single machine that he has.

Packer is decidedly against this idea. He cannot possibly hope to overcome the Cybermen with a single machine, and there are thousands more of the creatures heading for Earth now. Vaughn lashes out at Packer's pessimism and his insinuation that Vaughn is not in complete control. He screams at Packer to be quiet and obey, another rare crack of emotion in Vaughn's smooth veneer. They must go on and he is determined to think of something. They cannot take over Earth completely without more Cybermen. He orders Packer to activate the radio beam for the Cybermen to home in on.

In the UNIT aeroplane HQ, the Brigadier holds a briefing to update the situation. They have been unable to contact any other UNIT groups in any other country, nor any other UN military groups. The Cyber signal has successfully blanketed the world, putting everyone but themselves and Vaughn's men under control. They have no time to try and distribute neuristors worldwide; there are bound to be thousands of Cybermen heading for Earth as they speak. The Doctor's only suggestion is to try and knock out the control signal from space.

To do this, they'll need some sort of missile capable of reaching the moon. Checking his records, the Brigadier remembers that that Russians had a manned moon mission planned for countdown before the Cyber signal activated. That means that they'll be nearly ready for launch. If they can reach the rocket and replace the astronaut capsule with a warhead, they just might be able to hit the Cybership in orbit around the moon. The hardest part would be waking the Russian crewmen and then convincing them to help. The Brigadier realises it is their only hope and puts Captain Turner in charge of the mission.

The Brigadier then turns his attention to the additional Cybermen which the Doctor is sure will land on Earth shortly. Their ships will home in on a signal transmitted by Vaughn and so they can pretty accurately guess where they will land. The Brigadier suggests anti-missile missiles to shoot them down and confers with Sergeant Walters to try and find some nearby.

Zoe arrives with news of Jamie. He's gotten a flight flesh wound on his leg but he'll be fine. However, the doctor won't let him walk on it so he's out of commission for the time being. Professor Watkins too is fine and will recover completely. Zoe offers to help and the Doctor suggests she go with the Brigadier. He thinks that her remarkable brain may prove helpful as they try to deal with the incoming spaceships.

The Doctor decides that he must return to IE headquarters and talk to Vaughn again. He needs to buy time for his friends to enact their plans and this is the only way he can think of to do it. Zoe and the Brigadier both try to talk him out of it, certain that Vaughn will kill him, but the Doctor thinks he can handle things. He reminds the Brigadier that the Cybermen will most likely retaliate for any attack on their ships and he must find out what form that retaliation will take. He plans to take his radio with him and keep it on at all times so that his conversation with Vaughn can be overheard.

The Brigadier gives in, knowing that the Doctor is right. They could really use the inside knowledge that he could gain, as well as any delay. The biggest question is how he will get into the building, especially with all the Cybermen about. But the Doctor already has that figured out - he'll go through the sewers! There should be no Cybermen there now.

The Doctor drives away from the cargo plane in a jeep, headed for International Electromatix. A helicopter is despatched to stay in the area in case he needs it. Captain Turner is also ready to go. He has procured a supersonic jet and he and his men will head for Russia. They should be there in a couple of hours. Zoe will go with the Brigadier to the missile station at Henlow Downs Defence Base.

The Doctor enters the sewer system near the IE headquarters. He radios in to the Brigadier to let him know. He will switch his radio off until he reaches the building and will then call in again. The Doctor is comforted to know that a helicopter is standing by should he get into trouble.

Zoe is still concerned about how the Doctor will get through the sewers but the Brigadier dismisses her concern as idle worry. Sergeant Walters reports that Captain Turner is now airborne - ETA to Russia 2 hours, 7 minutes. The Brigadier seems invigourated by all of this activity. This he understands.

Vaughn and Packer pore over the invasion plans, noting the locations of all Cybermen in London. All the main communications centres are in the control of the Cybermen but they'll need the full invasion force before they'll be able to complete the takeover. Vaughn is confident they'll be here soon, and then there won't be a single city in the entire world that is not under his control.

Suddenly an alarm goes off and Packer jumps. He is nervous, certain that things are not going to Vaughn's plan. He worries that UNIT has infiltrated the building. Vaughn silences his nervous ramblings with a single word. To their surprise, the Doctor's face appears on the communications unit, addressing Vaughn. He says he'd rather like a word with him. The Doctor seems quite ingenuous and offers to show himself up to the office. He knows the way.

Packer is stunned; the Doctor must have a death wish coming here. However, Vaughn knows that this is not the case. The Doctor has clearly thought out his plan. He sends Packer to scour the building in case he's brought any UNIT people with him. For his part, Vaughn wants him kept alive for the time being as he still might have need of the TARDIS. He plans to sit down alone with the Doctor and chat.

On board the UNIT aeroplane, the Brigadier learns that they are only 2 minutes to touchdown and Henlow. The Doctor radios in that he is about to meet with Vaughn. He will leave his radio on as of now. The Brigadier wishes him luck and orders Sergeant Walters to tape the entire conversation. Walters is also in charge of getting the Doctor help should he need it as the Brigadier is off to the Defence Base.

Walters starts the tape as he hears the Doctor enter Vaughn's office...

In the office, the Doctor sits calmly in a chair whilst Vaughn stands at the window. The Doctor is trying to convince Vaughn of the utter ruthlessness of the Cybermen. They cannot be trusted to keep their bargains. Vaughn insists that he is in complete command of the operation and that he has the Cybermen right where he wants them. He feels that he is indispensable to their operation, having contacted them in deep space and provided the means by which they have travelled to Earth. He is the mastermind of the whole operation, which has been in the planning stages for 5 years.

It becomes clear to the Doctor that Vaughn is planning to double-cross the Cybermen and take over from them once the invasion is complete. He feels he is only using the Cybermen's might and numbers for his own purpose. The Doctor tries to reason with the confident Vaughn, reminding him that whilst the Cybermen here on Earth are conditioned to obey him and are therefore vulnerable, the thousands waiting in space are not. He cannot rely on Professor Watkins' machine to defeat the Cybermen. The Doctor knows that Vaughn has only one and without the professor he cannot make more. The Doctor's relentless logic begins to wear on Vaughn and he snaps, insisting irritatedly that he will be able to handle the Cybermen no matter what. Apparently there are chinks in his armour of confidence and the Doctor hopes he can exploit them.

The Brigadier and his men arrive at Henlow Downs Defence Base and find the crew unconscious, under the influence of the Cyber control signal. They set about fitting the men with depolarisers whilst the Brigadier contacts UNIT control by radio. He learns that Captain Turner is over the Russian border and that the Doctor is still talking to Vaughn with no trouble yet.

The CO of the base, Major Branwell, comes to, unsure of what is happening. The Brigadier greets him, urging him to clear his head quickly as they've got a lot of work to do.

The Doctor has become more irritated with Vaughn, trying to get through to him about the treacherous nature of the Cybermen. But Vaughn is back to his confident self, realising that the Doctor's main objective here is to play for time. Vaughn sidesteps his arguments and contacts Packer. It is now time to activate the homing beam and bring the invasion fleet to Earth. Whatever UNIT has planned, Vaughn tells the Doctor it is too late.

Branwell is brought up to speed by the Brigadier. He accepts the story despite the fantastic nature of an alien invasion. He has his Sergeant, Peters, check the radar for incoming ships. Nothing is showing, but the range of the radar is only 50,000 miles. This worries Zoe - the ships will be almost on top of them before they can be spotted. It will leave very little time to knock them out. Branwell and Peters prepare their missiles for launching so they'll be ready when the ships do show up.

The Cybermen report to Vaughn that the transporter ships will be launched in two waves, starting shortly. The Cybermen appear not to know that the Doctor is still alive and with Vaughn. The Doctor tries desperately to get through to Vaughn. He can't trust them to keep their word. He must know this. But Vaughn refuses to stop now, not when he is so close to success. He must go on!

Walters reports what he's overheard to the Brigadier - the Cyberman ships are on their way. He also reports that Captain Turner and his men have landed in Russia. No further word since then.

Major Branwell reports that there are blips appearing on the radar, just at the edge of their range. Faint but moving fast. It looks like the Cybermen. At this speed, they'll be within range of their missiles in just a couple of minutes. The missile countdown is held at 45 seconds while final checks are made.

However, as checks are being made, Zoe notices on the radar more ships coming in behind the first. The second wave. It is quickly clear that they haven't enough missiles to get all of the ships coming in and Branwell decides that they must simply get as many as they can, despite the obvious danger of this plan. Zoe has another plan. She has been doing some calculations in her head and she thinks that with a bit of co-ordinate reprogramming, she will be able to do maximum damage, getting 90% of the ships at minimum.

Branwell at first refuses her offer, saying there isn't time to calculate the co-ordinates, but Zoe insists she can do it herself, without a computer, in just 30 seconds. If they set the co-ordinates properly, they can start a chain reaction through the formation of ships and take them out. When the Brigadier insists, Branwell caves in and lets Zoe do as she suggests.

Zoe scurries from instrument panel to instrument panel, checking readouts and jotting down readings on a clipboard. In a few seconds, she has the answer and presents the new co-ordinates to Branwell and Sergeant Peters. Peters goes to feed the new information into the guidance computers whilst Branwell starts the countdown at 45 seconds.

As soon as Peters is finished, computer guidance control is activated and the missiles are ready for launching. The countdown continues from 28 seconds. When it reaches 10, Branwell inserts two keys into the firing panel and turns them. The safeguards are gone and the countdown reaches zero. All the base's missiles are launched into the air, heading for a rendezvous with the Cyberman transporter ships.

In space, the missiles reach their targets. Chain reaction explosions rip through the tightly-packed formation, destroying every one of the ships. Zoe was spot-on in her calculations.

In Vaughn's office, the Cybermen react to the attack. They blame Vaughn for betraying them and for the failure of their plans. But instead of giving up, they report that they will now take over the invasion. Vaughn is terrified of what this means for him and begs them to leave him in command. He promises he can quell this opposition but they will no longer listen to him. A pulse of energy issues from the Cyber machine and knocks Vaughn backward.

The Cybermen have a secondary plan. Clearly they have anticipated his betrayal. They tell Vaughn that a Cyber megatron bomb will shortly be detonated on Earth, destroying every living being.

Corporal Benton mans the radio in UNIT control and listens in to the Doctor and Vaughn talking. He has overheard the Cybermen order the use of the Cyber megatron bomb and knows it spells trouble for them all. He calls to the Brigadier at Henlow Downs.

At the Defence Base, the Brigadier and the crew of the base are celebrating their successful attack against the Cyberman transporter craft. Thanks to Zoe's spot-on mental calculations, they have been able to destroy all of them with a handful of missiles. However, Benton's news brings the celebrations to a halt. Of course the Brigadier has no idea what a Cyber megatron bomb is but he knows it's not good news. He and his team make ready to head back to control on the double. He leaves Major Branwell to monitor the skies for any sign of the incoming bomb.

Vaughn has recovered himself somewhat and now addresses the Cybermen via their communications machine. He tries to remind them that their bomb will destroy all the Cybermen already here on Earth but that, he is told, is a small sacrifice to gain control over the Earth. Vaughn is livid, spurred on by the Doctor's insistence that this was bound to happen all along. He grabs the cerebraton machine and activates it, pointed at the Cyberman communication device.

Vaughn is nearly mad now with rage and betrayal. He has long believed he could destroy the Cybermen with the emotion-generating machine and he decides to show them just who is the more powerful ally, aiming the device at full power toward the communication device. Somehow, the machine works on this device, there clearly being some vestige of living being inside the metal and wires. The Doctor tries to warn him against this action, but the maniacal Vaughn continues.

The machine explodes with a flash of light that knocks both the Doctor and Vaughn to the floor, completely destroyed. Vaughn staggers to his feet, surveying the destruction. He's very pleased with himself in a grim sort of way, but the Doctor knows that this is only a small part of the problem. Out there in space, the Cybermen are still planning to deliver a bomb which will wipe out all life on Earth. That is the real problem.

The Doctor tries to get Vaughn's attention but his mind seems to be broken. He has determined that the Cybermen will use Vaughn's homing signal to deliver the bomb and they must turn it off in order to stop them. Slowly, through the fog of betrayal and madness, Vaughn understands. He activates the communications unit and calls for Packer. To his horror, the blank metal face of a Cybermen fills the monitor screen.

Packer bursts into the office, terrified. The Cybermen no longer obey his commands and have turned on him and the other IE guards. He looks nervously behind him, knowing there are Cybermen following him. He can tell by the look in his leader's eyes that all is lost. Something has indeed been overlooked, despite all of Vaughn's assurance. Packer grabs Vaughn and shakes him, trying to find out what has happened. But it is all too late. A Cyberman enters the office and uses its energy weapon to kill Packer.

The Doctor dives to pick up the cerebraton machine from its place on the floor and manages to activate it before the Cyberman can fire again. The powerful emotional pulses swamp the creature's psyche and it falls dead on the floor, shrieking.

The Doctor, knowing they have little time, tries to find out from Vaughn where the radio beam is controlled. They must go there and turn it off themselves. But Vaughn is almost too frightened to move. His mind has snapped and all he can feel is fear. There are far too many of them to fight. They'll never beat the Cybermen. He now realises how futile his entire plan was. Five years lost. The Doctor raises his voice, trying to break through the madness in Vaughn's mind. At last he tells him that the signal is controlled from the factory compound, but he is certain it will be well guarded. The Doctor knows that they have to try and knock it out.

The Doctor calls the Brigadier on his radio. He has already overheard everything. The Doctor says they have two options: one is to knock out the radio transmitter or to destroy the main Cyberman spaceship before the bomb is launched. The Brigadier says that Captain Turner has reached Russia and the Russians have agreed to help. However, it will take at least 10 hours for the rocket to reach the ship. That leaves only the radio transmitter.

The Doctor turns to Vaughn and asks for his commitment to help in destroying the homing signal. He seems more lucid now, but his face is still dark and a new acidity has crept into his voice. He believes the effort to stop the Cybermen is futile and there is little incentive for him to help. If he assists the Doctor and the Cybermen are defeated, what will become of him? He is certain that he would be condemned by world opinion and punished for aiding the alien invaders. The Doctor tries to get him to stop thinking about himself for a moment and think of all the millions of people who will be killed by the Cyber megatron bomb.

Vaughn does change his mind, but not for the reason the Doctor would like. It has nothing to do with others; it has to do with him. With his hatred for the Cybermen. He wanted to take control of the world to bring it order, to impose a single will to save the world from chaos. He used the Cybermen for that purpose but now they have turned against him and destroyed his dream of an orderly and unified world. For that, they must be stopped. And he will help.

The Brigadier tells the Doctor he has a chopper nearby that can pick him and Vaughn up on the roof of the building and take them to the factory compound. The Doctor and Vaughn head for the roof, Vaughn making sure to take the cerebraton machine with him. He is looking forward to destroying the Cybermen guarding the radio transmitter.

The Brigadier orders their aeroplane to head toward the factory compound as well. He'll have to try and meet the Doctor there to help him. There will be an army of Cybermen against him and only a platoon of UNIT soldiers to assist. It will likely be some fight.

Captain Turner calls in from Russia, reporting that the Russians have already fitted a warhead to their moon rocket and it's nearly ready for liftoff. The Brigadier is sceptical that they'll actually have time to make use of the rocket, but it's in their best interests to chuck everything they've got at the Cybermen.

Major Branwell and Sergeant Peters at Henlow Downs have monitored this transmission. They, too, are sceptical. There just isn't enough time for the Russian rocket to reach the Cyberman spaceship before the bomb is launched. Peters somehow hopes against hope that there is still time.

In Russia, the moon rocket launches. Instead of astronauts on a survey mission, the booster carries a hydrogen bomb.

Corporal Benton receives the report of the launch, which he relays to a pleased Brigadier. He then receives a message from the Doctor on board the chopper. They are just coming in to land at the compound. The Brigadier tries to get him to hold off going in until they arrive, but the Doctor knows he cannot wait. They have no time to lose if they are to stop the bomb. The Doctor tells him that the transmitter controls are in the old IE factory on the east side of the compound. That is where the Brigadier should make for when he lands.

The Brigadier radios the chopper pilot and tells him to hover above the building in question once he's dropped off the Doctor. He can provide support if necessary and it will give the troops a reference point when they land. There is still 10 minutes before the UNIT aeroplane lands.

Whilst Benton puts the assault platoon on alert, Zoe and Isobel lobby the Brigadier to be allowed to come along. Amazingly, he agrees. Mainly so that he can keep an eye on them this time!

The Doctor and Vaughn wend their way through the maze of buildings in the factory compound, trying hard to avoid the Cybermen patrolling the area. They are nearly seen by one and Vaughn raises the cerebraton machine to destroy it but the Doctor holds him back. They still have the element of surprise for now. Kill one of the creatures and that is lost. They try another way to get round the guard.

However, their new path leads them straight into another of the creatures and this time they are seen. The Cyberman raises its weapon but Vaughn manages to activate the machine in time and the creature succumbs to the emotional waves. It collapses with an electronic howl. The Doctor knows he had to do it but he laments the loss of their anonymity. Vaughn suggests going over the roofs to avoid more Cybermen and the Doctor agrees.

Once on top, they can survey the entire area. Vaughn points out their destination, a non-descript brick building not far away. However, a whole squad of Cybermen stands guard outside.

Meanwhile, the UNIT aeroplane has landed and the Brigadier leads his assault platoon - along with Zoe and Isobel - into the factory compound. They see the helicopter hovering nearby and know that is the direction they need to make for. The platoon heads out, the Brigadier in the lead.

Unfortunately for the Doctor and Vaughn, Cybermen are also patrolling the roofs. Vaughn manages to destroy one, its body falling from the parapet to the ground below, but there are four more behind it. All they can do is try and evade them. Vaughn leads the way to a fire escape and the two men begin climbing down.

The UNIT platoon makes quite a bit of headway into the compound before they encounter their first Cybermen. Unfortunately, it is a large group facing them down the alleyway. A pitched battle erupts. Gunfire proves useful and even grenades are not entirely effective at killing the creatures. Finally, the Brigadier calls for a bazooka which knocks all of the creatures out of the way, if not outright destroying them all.

The Doctor and Vaughn can hear the sounds of battle but have little time to pause. Hopefully this is just the distraction they need to reach the radio transmitter.

At last, the bazooka fire clears the way and the UNIT platoon can move forward. It was a hard fought victory over only a handful of the creatures. It will be much harder if there are more ahead. As the soldiers move off, Isobel hangs back, snapping frame after frame of the dead Cybermen littering the ground.

At last the Doctor and Vaughn reach the old factory building. Strangely there are no Cybermen about. However, Vaughn doesn't want to hang around and wonder. He climbs a short ladder to a landing which leads to the control room door. The Doctor hangs back, somehow sensing danger, and he is not wrong. Three Cybermen emerge from hiding and prepare to fire at Vaughn. He is able to destroy two of them using the cerebraton machine, but the third one manages to fire first, catching Vaughn squarely. He is killed instantly by his former allies, dropping the machine.

The Doctor flees, barely managing to stay one step ahead of the Cyberman as it fires after him. Racing away from the Cyberman, the Doctor runs right into the Brigadier and his men, approaching from the other end of the alley. Assessing quickly, the Brigadier orders the Doctor down and then a bazooka fired at the approaching Cyberman.

The Doctor does as he is told and the bazooka destroys the Cyberman. The Doctor is fine and tells the Brigadier where to find the radio transmitter controls. He and his men move off to destroy it, leaving the rattled Doctor to collect himself. Isobel rushes up to him, snapping pictures of him as he sits there on the ground. The Doctor is lured into posing as prettily as possible.

A short time later, the UNIT platoon is back in the aeroplane HQ, victorious. The Brigadier reports the situation to all units via radio. The radio transmitter has been destroyed so the bomb cannot be delivered, but the Cyber signal is still being broadcast and so the world is still under Cyber control until their spaceship can be destroyed.

At Henlow Downs, Sergeant Peters listens to the message but he is also keeping his eyes on the radar screen. Suddenly he sees a large contact at the farthest range of his radar, something very large and stationary. It must be the Cyberman spaceship. Major Branwell interrupts the Brigadier's message to tell him the news. The contact is at 50,000 miles, just outside of their missile range but just inside the radar's range.

The Doctor is certain it is the Cyberman spaceship but he cannot initially deduce why it has moved in from its location around the moon. Perhaps it is trying to avoid the Russian rocket, but more likely they have determined another way to deliver their Cyber megatron bomb. With the homing signal out, they had to move closer to Earth to accomplish their goal. Zoe realises that this manoeuvre has brought the Cybership very close to the Russian rocket, but more likely the two have passed on the way. The Russian rocket is already heading away from its target!

The Brigadier contacts Captain Turner in Russia. They have noted the movement of their target as well and are working to try and turn the rocket around. They can do it, but it will still take over 12 minutes for the rocket to reach the spaceship, plenty of time for the Cybermen to launch their bomb and move away... if they are ready.

All that the nervous humans can do is wait and hope.

After what seems like an eternity, the radar crew at Henlow Downs spots the Russian missile on radar. It is on target. However, there is a third echo on the radar. It must be the Cyber megatron bomb!

The crew at Henlow Downs races into action, readying a new barrage of missiles to try and shoot down the bomb. They have very little time. Branwell reports all this to the Brigadier. They stand a good chance of shooting down the bomb, but it will be a race against time.

The crew track the progress of the bomb and ready a missile to attack it as soon as it's in range. A tense few seconds pass and Branwell launches the missile. It is quickly obvious that their aim is off and the missile is going wide. Branwell orders a second missile quickly prepared and he fires again. This time, its aim is true and the crew watch the radar breathlessly as the missile converges on the Cyberman bomb. They've done it! The radar shows no echo in the vicinity of the bomb. The Earth is safe.

Before Branwell can reach UNIT control to report this, Sergeant Peters shouts out. The Russian rocket is nearly on top of the Cyberman ship. To their amazement, the ship has not moved.

The rocket hits the ship squarely and it is completely destroyed. The Cyberman invasion of Earth is ended and the humans are released from Cyber control.

Some time later, things have returned to normal. Isobel is in her makeshift studio, shooting pictures of Zoe in her glittery catsuit. This is sort of a farewell performance for Isobel as she is done shooting models and is off to start a new job. As a result of her work photographing the Cyberman, she has landed a job with a publishing group. She'll be a globetrotting photographer soon.

Next for Zoe is back to traveling, as soon as the Doctor is done repairing the TARDIS circuits that is. Isobel wonders where they'll go, but of course Zoe has no answer for that!

Captain Turner arrives to announce that the Doctor is actually ready to go now. He is going to drive them, stopping by the hospital to pick up Jamie who is convalescing from his gunshot wound. Isobel asks to come along and Turner is glad to have her. Clearly a relationship has developed between the two.

A short time later, a jeep pulls up next to the pasture where the TARDIS landed what seems like weeks ago. All is quiet and the field is empty. Isobel and Captain Turner cannot understand why they want to be let out here but the Doctor, Jamie, and Zoe hop out and enter the field. They bid each other goodbye and the Doctor leads the way to the TARDIS. Only, the TARDIS is still invisible and the Doctor has a hard time finding it.

After a bit of searching, the Doctor stumbles onto it by accident, his hand nearly disappearing as he touches the invisible ship. He finds the door and enters, also disappearing. Isobel and Turner watch all this with growing concern. After a moment, a rough engine sound issues across the field and the TARDIS appears.