The TARDIS is in flight but Jamie seems to care very little. His thoughts are with Victoria, now gone. Left behind on Earth in an unknowable future. Even when the Doctor announces that they're landing, Jamie barely responds. The Doctor activates the scanner but it is blank. This seems to pique Jamie's interest a bit and tries to help the Doctor at the controls.

Nothing seems to work, even though there's no fault indicated. The Doctor turns to the other instruments and they all register normal atmosphere outside. There is a large amount of metal all around them however. Shortly, a picture begins to form on the screen. It is an idyllic scene of lakeside beauty. Jamie is pleased. However, the picture changes as they watch and displays a giant waterfall lit by moonlight. And again, this time to a bright sandy beach.

The Doctor is certain none of these pictures represents what is really happening outside. The readings clearly indicate otherwise and he deduces that they are temptations. The TARDIS is trying to warn them to get away from here to somewhere more pleasant. But before they can do anything, a serious fault develops in the console. The power lines are overloading!

Smoke begins to pour from the console despite the Doctor's best efforts. Part of the console explodes and the Doctor announces that the fluid link is gone! They both begin coughing as the mercury in the link begins to vapourise. They've got to get out of the TARDIS, and quickly. They make their way to the door, struggling to see through the smoke. The Doctor removes a rod-like device from a hidden panel and when he does so, the entire ship begins pulsing and rocking. He and Jamie manage to get out but something terrible has happened to the TARDIS.

Outside the TARDIS is an empty, metal-walled corridor. The Doctor and Jamie emerge, still coughing as they breathe in the clear air. The Doctor explains to Jamie that the rod-like device he disconnected was the time vector generator. Once removed, the interior dimensions of the ship returns to that of an ordinary police box. If he had not done so, the mercury vapour would have killed them both. Jamie doesn't understand much of this, but he's grateful to be alive.

Looking around, the Doctor decides they must be in the motor section of some kind of rocket. It must be meant for living beings because the atmosphere is good and there is an artificial gravity system keeping them on their feet. Jamie is interested in finding water, which the Doctor thinks is unlikely here. The Doctor has noticed that there seems to be no movement around them. Perhaps this rocket is on the ground. The Doctor gives Jamie a lemon sherbet to quench his thirst and they move off to explore.

The rocket appears completely deserted and Jamie cannot understand why the TARDIS was trying to warn them off. It seems unlikely there's any danger here. The Doctor spots an oil track running along the corridor and they follow it. It must have been left by some sort of machine...and very recently. Perhaps they're not alone after all.

They activate a door control and move into the next section where the oil track continues. They follow it up to another closed door but the Doctor does not move to open it. He worries about what may be on the other side. Near the door is a monitor screen which, once activated, shows a view of the room beyond the door. It appears to be a control room of some sort, but it is completely deserted.

Feeling that it's safe enough and curious about why the TARDIS sensed danger here, the Doctor decides to try and open the control room door. However, it is not as easy as the interior doors. It stays obstinately shut. The Doctor and Jamie spread out to explore two other doors leading off to the side of the corridor.

Jamie finds only a store room, but the Doctor finds living quarters. They go inside. Clearly this was put there for a human crew, but where are they? Jamie forgets all about this when he finds a food dispensing machine, including a button marked "water".

Inside the shadowy control room, there is movement. It is not a living being but a robot, squat and round with lights for eyes. It moves out of the shadows, alerted to the presence of people on board, and heads for the door. As the robot approaches, the door slides open. The robot trundles out.

In the crew cabin, the Doctor and Jamie assess their situation. The Doctor has ascertained that this rocket normally carries four crew members, two on duty and two off. Where are they? Jamie is still wondering why the TARDIS tried to warn them away. Clearly there's nothing wrong here. The Doctor, however, disagrees. Looking out the observation port he can see that the rocket is just drifting aimlessly in space, going nowhere. But that doesn't sound like terrible danger to Jamie. He suggests they just replace the rod thingy in the TARDIS and take off.

The Doctor reminds him that they still have no mercury with which to refill the time vector generator so they cannot leave. They both agree that there must be mercury somewhere on the rocket but the Doctor is still worried about the crew. Jamie believes the answer to both problems lies in the locked control room.

The robot continues its slow, methodical trek through the rocket's corridors.

The Doctor and Jamie have completed a search of the rest of the rocket, apart from the control room. They've found no clues and no mercury. They decide to have a little rest before trying to tackle the control room door again. Jamie wants some food and the Doctor sets out to oblige him, working the food machine like a pro. He whips up a meal of roast beef and vegetables for Jamie and some pork for himself. To Jamie's horror, the machine produces odd-looking food cubes in place of a pile of food. He is dubious to say the least.

They tuck in but Jamie's mind is elsewhere. He wonders what Victoria is doing right now. The Doctor tries to distract him with a lecture on the relative nature of time, but Jamie presses him to answer. He tells Jamie, as best he can, that Victoria chose a very good period in which to stay. Few wars, great prosperity, etc. She'll be happy enough.

The Doctor suggests they let their meal digest before going to the control room, so Jamie decides on a wee lie down. The Doctor continues to speculate on the fate of the crew. Perhaps it was some disaster. Hopefully they'll find out once they get into the control room.

The robot continues on down the corridor, almost like a bloodhound searching for clues. It seems to know there are intruders on board but it is taking its time to track them down.

The Doctor gazes out the observation port again, making sure their drifting path won't lead them to any danger. It looks safe enough, he tells Jamie, but the lad is already fast asleep.

The robot reaches the motor section and finds the TARDIS there. This is clearly a foreign object and it decides to seal it off from the rest of the ship. Backing through the door, the robot activates a control and the door slides shut. It produces a laser torch and welds the door closed. The intruders have been isolated from their craft.

The robot turns and heads back to the control room.

In the silence, the Doctor hears some noise in the corridor outside the crew room. He goes to the closed door and listens carefully. As the noise fades, he cautiously opens the door. There is no sign of anyone but he does notice that the oil track is now larger and covered with fresh oil. Something has been here.

The Doctor returns to the control room door, still firmly closed. He activates the monitor again, but it shows only static.

Inside, the robot settles itself into the command area. Using its probes, it connects to the controls. The dials and instruments light up. The engines fire quickly to life and the ship lurches suddenly to one side.

In the corridor, the Doctor is caught unaware and thrown hard against a bulkhead. He slams head first into the wall and collapses to the floor.

The rocket comes to life from its drifting slumber, changing course in space.

Jamie, too, is tossed about, falling from his bunk. He gets up quickly and heads outside, looking for the Doctor. Jamie sees him slumped on the floor and runs to him. The Doctor is dazed and in great pain. It seems as though he may have a concussion. He manages to tell Jamie that there's someone in the control room and thinks they should get back to the TARDIS. Even without the mercury for the time vector generator, it will still be the safest place.

Jamie helps the Doctor up and they stagger down the corridor to the motor section. The door is locked and won't budge. Jamie notices the weld marks and knows immediately they've been effectively shut out. The Doctor clutches his head and staggers. Jamie helps him back to the crew cabin, feeling distinctly uneasy about all of this.

Once in the cabin, the Doctor urges Jamie to close and lock the door. He does so, but when he returns to the Doctor, he finds his friend unconscious. Jamie cannot rouse him. He is alone.

In the control room, the robot disengages the engines and the rocket falls silent. It resumes drifting on its new course.

The robot then turns its attention to a group of egg-shaped white pods in the rocket. It activates several controls and the pods seem to come to life. They move toward an airlock, seemingly of their own accord. Once in the airlock, they are ejected into space one by one. They drift together away from the rocket.

In the distance can be seen the pods' objective - a giant, wheel-shaped space station floating in space.

Jamie sees the giant silver station as well and is awed by it. So captivated is he that he does not notice the dazed Doctor rise from his bunk and leave the cabin.

The Doctor stumbles into the corridor, his one thought to free the sealed door to the motor section and gain access to the TARDIS. He reaches the door and produces the time vector generator from his coat. When he activates it, one end lights up and he points the powerful energy at the welded edges of the door. However, he does not get very far before he is set upon by the robot.

The little machine bears down on the Doctor, who is completely trapped with no avenue of escape. Concussed and dazed, the Doctor can do nothing. He presses himself against the door.

Jamie finally notices the Doctor's absence and is very worried. He hurries out into the corridor. At the end he can clearly see the robot menacing his friend. He must act quickly. Returning to the cabin he grabs a blanket from one of the bunks. He flings it over the head of the robot, disorientating it. Jamie grabs the Doctor and hauls him back to the cabin, closing and locking the door. He helps the Doctor to lie down on the bunk once again.

Using its weapons, the robot frees itself of the blanket, destroying it in the process. It quickly trundles to the cabin door and begins trying to burn its way in.

Jamie is beside himself with worry. They have no weapons and no means of escape. The door will clearly not hold for very long. The Doctor gives Jamie the time vector generator and, hazily, tells him it can be used as a weapon, like a gun. But he must be careful. That is the extent of the instructions and Jamie is left to figure the rest out for himself. He has little time to do so as the robot has nearly burned through the door.

Figuring out which end is which, Jamie aims the generator rod at the widening hole in the door and activates the device. To his great amazement, it works immediately and spectacularly. The robot is completely destroyed, its many pieces scattering all round the corridor. He can hardly believe it himself but is very glad it worked. He turns to celebrate with the Doctor, only to find his friend collapsed on the bunk, completely unconscious.

On board the space station - nicknamed "the Wheel" - is a multinational group of scientists with many varied specialities. They are under the command of one Jarvis Bennett, their stern Controller. At the moment, all of the crew members are focused on one thing - the rocket which is drifting toward them. Leo Ryan is Australian, Dr. Gemma Corwyn is British, and Tanya Lernov is Russian. They work together with Italian technician Enrico Casali to get a firm fix on the rocket. They had noted its presence some time ago, when it was still moving under power. They are quite concerned now that it has halted and is apparently adrift. There is no radio contact, which is even more worrisome.

Bennett reports that he's identified the craft as one Silver Carrier, a supply ship for Station Five that was reported overdue nine weeks ago. It is almost 90 million miles off course! Armed with this information, Rico tries again to initiate radio contact.

They are all certain the rocket couldn't have drifted all this way from Station Five. Someone must have been on board at some point. They are being very cautious, trying every means at their disposal to make some contact before giving up. It could have been a faulty automatic pilot system that brought them here, the crew long dead, but that is just one of a dozen possible scenarios.

All attempts at communication have failed and Bennett is very worried. If he's right and a faulty automatic pilot is to blame, that rocket's engines could suddenly activate and drive it straight into the station! He thinks hard about their next move.

In space, the egg-like pods float unseen between the Silver Carrier and the Wheel. They hit the outer hull and attach themselves. This is no accident.

Tanya registers the impacts, along with a corresponding drop in air pressure inside. She thinks they might be meteorites, a common occurrence here, but they had no warning. It seems unlikely. Bennett thinks it insignificant as there's no real damage but Tanya is quite concerned. The Controller, however, is much more worried about the sudden acceleration scenario. He can't take the risk of damage to the Wheel and decides to destroy the Silver Carrier using their mighty x-ray laser!

The barrel of the weapon rotates on it axis and points directly at the rocket.

The crew of the Wheel bustles about in anticipation of the destruction of the Silver Carrier. It is an unprecedented event, to use the x-ray laser on another ship. It is normally used to destroy dangerous meteorites. Controller Bennett even wants to make a video recording of the event. Tanya sets up the equipment. Everyone readies for their part in the operation, but Dr. Corwyn wishes to speak to Bennett before the firing. She insists... and he cannot say no. They go to his office.

The remainder of the crew watch as they go, their excitement undimmed. Leo Ryan, in particular, seems to be enjoying himself, Bennett's enthusiasm rubbing off on him. However, he worries that Dr. Corwyn, a notorious "stick in the mud", will try and talk him out of it. Tanya chastises him gently, saying that Gemma is right to be cautious. Leo doesn't agree. That ship is more than 80 million miles off course. There can't be anyone alive on board.

He is of course wrong about that. Jamie and the Doctor are very much alive, and Jamie would like them to stay that way. He has seen the large barrel protruding from the space station, pointed straight at him, and is desperate to do anything he can to stop what he knows is about to happen. The Doctor, still unconscious after the severe blow to his head, turns on his bunk, causing the time vector generator to fall.

Jamie helps his friend to lay more comfortably, then picks up the rod-like device. He remembers how the Doctor told him it was a weapon and he remembers what happened to the robot when he used it. Perhaps it can help them now...

Bennett explains once again his reasons for destroying the rocket, the safety of the Wheel being uppermost in his mind. However, Gemma reminds him that they can't be certain there is no one alive on board, and she thinks he is overstating the possible danger. Bennett thinks she's just upset because he's enjoying the process of destroying the rocket.

She knows that he assumes there was some tragedy on board, that the crew was killed, and that the automatic pilot engaged to send the rocket here, but it doesn't make sense. Why didn't the auto pilot take the rocket to Station Five, the station it was meant to serve? It takes Jarvis some considerable supposing to make a case against this and his argument begins to erode. Gemma reminds him that it would be very easy for them to go over to the Silver Carrier and check all this out. Bennett, however, reminds her of the danger to the Wheel if that rocket should suddenly accelerate. Sounds like stalemate.

Jamie takes the rod-like time vector generator and points it out the window. He's not sure what he's hoping will happen, but it's the only chance he's got. He aims the business end directly at the space station and activates it. The tip lights up but there is no apparent reaction.

However, on board the Wheel, there is most definitely a reaction: the communications system erupts in an ear-piercing squeal of interference. The communications officer rips off his headphones and grabs his head in agony. Everyone can hear it and all the indicators all over the station are in the red zone. Tanya races off to fetch Bennett whilst the others help the dazed communications officer.

Meanwhile, Leo has been listening to the deafening noise. It is still ear-piercingly loud, but he thinks he has discerned a pattern to it.

Bennett is still arguing with Gemma when Tanya bursts in. She reports what has happened and Bennett knows immediately the "attack" is coming from the rocket. Proof positive that it is a menace. They all hurry back to the control room.

Jamie continues to "fire" the generator at the station. The pulses are meaningless, but they are in a regular pattern. He's clearly not doing any damage but he can only hope that at the very least someone can see the light coming from the window.

Bennett takes command, ordering Tanya to pinpoint the source of the interference. He despatches Dr. Corwyn with several other crewmen to take the communications officer to the medical bay. That done, he decides to waste no more time in destroying the rocket. He orders officer Bill Duggan to fire as soon as he's ready.

However, Tanya's shout belays him. She has confirmed a pattern to the interference. It's not any known code, but the repetitive order seems deliberate. It must be. Bennett is angered at being stopped once again, but he knows he can't take action if there's a possibility that someone is alive on that rocket. After a moment's checking, Tanya confirms that the interference is coming from the rocket.

Showing he is not just a single-minded leader, Bennett abandons his plan and orders two men sent via spacewalk to the rocket to investigate it. There must be someone on there. But if they're nine weeks overdue from their destination and 80 million miles off course, they must be in a pretty bad way by now.

Jamie has seen the astronauts floating through space toward him and has stopped "firing" at the station. He keeps an eye on the Doctor as the two men arrive and enter through the airlock. Jamie greets them, directing them to the injured Doctor.

A short time later, all of them are safely aboard the Wheel, being looked after by Dr. Corwyn. Work aboard the station resumes at last. It's primary mission is to monitor meteorite storms in space and to warn Earth and any passing ships. An officer called Laleham reports a storm to incoming ship Voyager 5.

Meanwhile, talk of the new arrivals passes among the crew. Leo notices a problem indicator on one monitor and learns from crewman Chang that they continue to have unexplained readings along the hull where those supposed "meteorites" hit earlier. The problems can't be traced because they disappear too quickly, but they are all noted in the log. It appears to be a day for mysteries here.

Leo notices a look of worry on Tanya's face and inquires of her. The unexplained pressure drops are still of concern to her, along with Chang's report. She can't trace the pressure drops either and Leo agrees that a total check of the air supply unit is called for. However, she fears that all these unexplained problems may stem from the arrival of the rocket. The two newcomers weren't exactly normal.

Leo tries to sooth her concern, offering his hand for her to hold if she gets scared. Leave it to him to hit on a girl when she's frightened!

Outside, more of the egg-like pods drift from the Silver Carrier to the Wheel, attaching themselves to the hull.

In Dr. Corwyn's office, Jamie's examination is complete. He is in fine physical shape. The Doctor, however, is definitely suffering from a concussion. She is still waiting for the x-rays to determine if there's any skull fractures.

Gemma tries to ascertain what Jamie and the Doctor were up to on the rocket, likening their clothing to fancy dress. Jamie takes exception to this and becomes guarded. He provides his own full name, but decides to call the Doctor "Dr. John Smith", a name he picked up from the manufacture of a piece of equipment in Gemma's office. In response to her scepticism, Jamie tells her there "must be a lot of them about".

Gemma tries to press Jamie to find out what happened on the rocket, how it got off course and what happened to the crew. Meanwhile, she gets Jamie a requested glass of water. Jamie tries to be vague but she won't let it go so he invents a story about a raging fever he had. He was insensible for days and when he woke up, the Doctor was hurt and all the doors were sealed shut. He doesn't know how it all happened. It seems clear that Dr. Corwyn doesn't buy this story, but he hopes that he's at least bought some time until the Doctor wakes up and can come up with something better.

Jamie is free to go, but she tells him that the Controller will want to speak with him. They'll also have to organise some way of getting him home. There should be a ship passing through in a week or two. Jamie scoffs at this, of course, knowing he is a very long way from home. He starts to go, leaving most of his water, a fact that Gemma notices with keen interest.

She stops him from leaving and suggests that he might like a tour of the Wheel. He agrees, having nothing else to do. She directs him to the para-psychology library and someone named Zoe. She is the librarian there and will show him around. Jamie goes off, making sure that Dr. Corwyn will keep him updated on the Doctor's recovery.

Gemma calls Zoe, a youngish girl with keen eyes and a dark pixie haircut. She tells Zoe that one of the refugees from the rocket is coming to find her. However, Zoe is not only to show him around but also to observe him. Discreetly. She wants to know more about him and his friend. Zoe agrees, although she is a bit distracted by a very complicated problem she is completing in her head. She seems a bit like a human calculator!

Eventually, Jamie finds his way to the library where Zoe is busily recording a report about an imminent nova explosion of a star in the Messier 13 cluster. It would be a repetition of the phenomenon observed in the Perseus cluster just last week. She breaks off when the oddly-dressed Jamie arrives and she even giggles when she sees his "skirt". She cannot contain her glee and accuses him of wearing women's clothing. He explains his kilt and his Scottish origin, but now she thinks him a barbarian. Annoyed by all this, Jamie threatens to put her over his knee and "larrup" her.

As if she were in the presence of living history, Zoe seems genuinely pleased to be able to show Jamie around. Perhaps things are just a bit too prim and proper here in her time. She hurries off to show him something about "interstellar flora". Jamie must struggle to keep up with the energetic girl.

They reach the power room where Bill Duggan, another Australian, works. However, he has also created a makeshift greenhouse down there where he grows exotic plants, including a species all the way from Venus. Duggan explains that the Controller was very much against his little plant kingdom but Dr. Corwyn convinced him to allow it. Good for the mental states on a long space posting.

From there, the tour moves on to the actual machinery of the power room. Duggan proudly shows off the capacitor bank for the x-ray laser. It is a weapon they use against meteorites. They also have an anti-magnetic deflector for the same purpose. Of course, much of this conversation is lost on Jamie, although he knows the Doctor would be interested.

Zoe takes the opportunity to inquire about the Doctor. She learns that he is a scientist, but Jamie cannot specify which type. He assumes the Doctor knows something about all types! Zoe asks when the Doctor will be up and about. Jamie only wishes he knew the answer to that one.

Dr. Corwyn is reporting to Bennett on her examinations of the Doctor and Jamie. She also does not know how long it will be until the Doctor is up and around. If all he's got is a concussion, it shouldn't be long. Bennett hopes that is the case. He doesn't like mysteries and he can see that this one is starting to effect crew efficiency. Routines are essential for crew members on deep space missions, he says. Unexplained incidents are disruptive and mean trouble. For Jarvis himself, he is trained for emergencies, for mysteries. It's just business as usual for him.

Gemma continues her report on Jamie. She is convinced that he is lying about what happened to him on the rocket. Not completely, she says, and apparently reluctantly. He never had a fever; his physical showed him to be in very good health. However, he clearly hasn't been in space very long. Certainly not the nine weeks that the Silver Carrier has been missing. She's also sure that the Doctor's name isn't "John Smith". On top of that, Jamie asked for a glass of water and then left it. No one with space training would ever do such a thing - water is too precious in space. She suspects he is a stowaway or, worse, an "agent".

Bennett seems to seize on this. Many people on Earth think that the space programme should be abandoned and humans should simply stay on Earth. They have already done some damage. Bennett fears sabotage could be the motive of these strangers. Perhaps they even did away with the crew of the rocket.

Gemma tries to reel the Controller back from these paranoid thoughts, but he is certain he's right. It all fits together for him, including the pressure drops and the "attacks" on the hull. She cannot believe that he's leaped to this conclusion but can say nothing to keep him from racing out of her office. He is determined to stop these saboteurs before they do any real damage.

Jamie's tour concludes in the operations and communications room, where he is told that the Wheel acts as a relay for Earth as well as ships in deep space, and it is an early warning system for space phenomena like meteorites. Jamie is of course baffled by all of these details. However, he does understand when Leo Ryan announces that the destruction of the Silver Carrier is going ahead. He learns how close he was to being blasted by the x-ray laser earlier, saved only by the "message" that he sent using the time vector generator. Now that Bennett is sure there's no one else on board, the destruction can go ahead. Jamie is understandably worried. The TARDIS is on that rocket!

All of the crew members take their place and get ready to perform or simply watch the firing of the x-ray laser. Even Zoe is drafted to help out. Jamie, seeing that no one is paying attention to him, slips away and out the door. He makes directly for the power room, remembering Duggan's information about the capacitors that control the laser gun.

Bennett makes for the control room and finds his staff ready for the firing. However, no one knows where Jamie is. Clearly he has slipped away from them deliberately. Bennett is angry and has Duggan retrace their tour. As soon as he learns that Jamie was shown the power house, he knows that this is where the saboteur will be found. Deciding to keep things quiet, Bennett confides only in Duggan and Zoe. They are to say nothing to anyone else, but Duggan is to follow Bennett in a moment or two. The Controller hurries out of the room.

Leo and Tanya have noticed the commotion but both Duggan and Zoe keep quiet. This does not appease the curious Tanya. She corners Leo and tells him about her famous nose. When it smells trouble, it's never wrong. She can certainly smell trouble now - and it's coming from that rocket!

Tanya Lernov has no idea how right she is. However, she cannot know the true nature of the trouble she senses. On board the Silver Carrier, two more of the egg-like pods sit in the control area. A countdown clock reaches its end and suddenly the pods come to life. They begin pulsing and glowing.

Soon the energy level reaches maximum and the inside of one of the pods can be seen. A humanoid figure is inside, beginning to move and stretch. It is as if the creature is just now coming to life. It stretches its arms upward toward the shell of the pod.

On board the Wheel, the crew is unaware of the danger that has awakened on the Silver Carrier. Leo Ryan continues to sweet-talk Tanya despite her serious warnings of danger on the rocket. He assures her that the x-ray laser will shortly put paid to any problem it may pose.

In the power room, Jamie is desperate to put the x-ray laser out of action. The TARDIS is on board the rocket and will be destroyed with it. On a shelf, he finds a ball-shaped spray canister. He has no idea what is in it, but it is all he can find. Opening an inspection panel to the innards of the capacitor bank, Jamie sprays the stuff down inside. It is a filmy white substance that coats the machinery thickly.

Bennett bursts in, along with Duggan, to catch him in the act. They grab him and pull him away from the machinery. Duggan grabs another spray can and tries to wash out the film, a quick-seal plastic. It is too late. Bennett is livid and is absolutely convinced now that Jamie is a saboteur whose aim is to put an end to Earth's space programme. And he has done a pretty good job. Duggan reports that the x-ray laser is completely wrecked. Jamie tries weakly to explain, but he really can't. He's not even sure what he's done. He tries at least to be cooperative with his captors.

Bennett issues an announcement station-wide, ordering all security officers to take up sidearms at once. Easy-yellow security plan is now in effect. A security detail is despatched to the power room as well.

In the operations room, Tanya takes this as confirmation of her senses. She knew there was trouble. On top of all of this, Zoe has reported to Leo her belief that one of the starts in Messier 13 is about to go nova. Trouble is piling up.

Two Cybermen now occupy the control area of the Silver Carrier. They activate the communications equipment, connecting to another, much larger ship further out in space. They report to a machine-like Cyber-planner. Phase one and two are complete. Cybermats have been launched. The Cybermen are undetected on the rocket and phase three is ready to begin.

Dr. Corwyn has also learned of Zoe's nova prediction. As always, she is sceptical, but Zoe is convinced she is correct. She has a highly-trained mind and doesn't make mistakes. Gemma is also concerned about the security alert and moves off to check it out.

Duggan reports to a furious Jarvis Bennett that Jamie has done severe damage to the laser controls. All of the primary relay conduits are fused shut by the plastic and the entire unit will have to be stripped down. It could take as long as a week to rebuild the unit. Jarvis hits the roof, and is not subdued when Dr. Corwyn arrives.

Jamie denies the charge of sabotage, but Bennett is convinced. He must be one of these "pull back to Earth" nuts and he must have friends ready to attack once the laser is out of order. However, there is a more immediate problem. Gemma reports Zoe's prediction to Bennett. The radiation fallout from the nova explosion will swing the Perseid meteor shower right down on top of the Wheel. With the x-ray laser, they could knock out many of them before they arrive. Now, they are helpless.

Bennett has Jamie dragged out and orders Gemma to confirm Zoe's calculations with a computer. They must know for certain what is going to happen.

Duggan sets to work immediately on the laser machinery. It is going to take all he's got to fix this lot. After a moment, he is distracted by some movement at his feet. A strange creature - like a large metal bug - slides across the floor toward him. He is amused by the creature, with its bug eyes and strange gliding movement. Must be some sort of "space bug". Hearing footsteps approaching, he hides the creature, nicknamed "billybug", in one of the storage closets. He is afraid that any more unexplained arrivals will make the Controller go spare. Little does he know, he has handled a deadly cybermat!

Another crew member enters and they set to work.

In the operations room, work begins on confirming Zoe's prediction of a nova explosion. Gemma tries again to get Jamie to explain why he sabotaged the laser. He apologises again but won't explain why he did it. He seems at see in the face of all the questions. This is the Doctor's area and he's no good at making up stories. He tells them that he simply had to stop them destroying the rocket. Helplessly, he says that the Doctor told him to protect it.

Some time later, the Doctor is recovering in a medical bed, listening to Jamie sheepishly explain all that has happened. The Doctor seems quite irritable and out of sorts. He doesn't even seem to approve of Jamie's actions in stopping the destruction of the rocket, let alone leaving him to get them both out of trouble. Making things more difficult, the Doctor doesn't remember much of what happened on the rocket. Not even the robot that attacked him. He does, however, have a feeling of great danger. Something that he saw or felt on the rocket. If only he could remember...

On board the rocket, the Cybermen report to the Cyber-planner. All phases are proceeding as planned. Time to prepare phase four.

Computer data have confirmed Zoe's prediction of nova activity. It will happen just as she's said, including the meteorite deflection. It is oddly similar to an event that occurred in the Hercules cluster just last week. Except this time, they don't have the x-ray laser to defend themselves against the bombardment. What's worse, Enrico reports that the radiation and the meteorites are four magnitudes higher than the last one.

Tanya is now very worried. Without the laser, they are defenceless. Leo thinks that their anti-gravity force field will protect them, but Zoe assures him this is not the case. The meteorites will be 200 tons each. She says this with great precision and a matter-of-fact tone which irritates Leo. He accuses her of being a robot, spouting facts and figures with little regard to the fear that it may engender in the crew. He stalks off to see Bennett, saying that Zoe is "all brain and no heart".

Duggan is helped by two crewmen, who remove a large section of the capacitor machinery. They take parts away for repair and he is alone. As they go, he notices his "billybug" loose on the floor again, the door of the storage closet open. On the floor are a large pile of metal rods, all of them with the centres eaten away. They are just husks. Duggan becomes alarmed when he realises what has happened.

The metal is bernalium, a vital component in the operation of the x-ray laser, and every last rod has been eaten. There are a dozen boxes of the stuff in the closest, and they are all the same. The cybermat has eaten them all. Duggan is startled when a crewman enters. He tries to hide the cybermat but finds that it has already gone. Duggan says nervously that everything is going well and then sends the crewman to go and check spares for their bernalium stock. He is hoping against hope that there is more on the Wheel.

The crewman leaves to obey the order and Duggan turns back, trying to find his "billybug". He's ready to murder the little pest. However, it is nowhere to be found. Duggan turns back to work, unaware that there are now two cybermats in the room with him...

Dr. Corwyn completes the Doctor's physical exam and pronounces him healthy. However, he can't get up just yet, a fact which suits him just fine. He admits that he is experiencing some memory loss, but that is to be expected with concussion. As long as he's not anxious about it, he'll be fine. The conversation turns to why the Doctor wanted the rocket protected and he is quick to answer. He assures Gemma that they are not saboteurs and are indeed very grateful to the crew for rescuing them.

However, Gemma tells him about the oncoming meteorite storm and how the damage to the laser has left them in a very vulnerable position. Jamie protests that he didn't mean to do this. He didn't even know about the meteorites when he put the laser out of action. He still doesn't even know what they are!

They are interrupted by the arrival of Zoe. She is full of questions and hopes to get answers from the Doctor. He is concerned to hear that there is a guard posted on their door, but he is quite taken by the diminutive astrophysicist, despite her know-all attitude. She wants to know how he was able to pilot the rocket 87 million miles off course in just nine weeks. To her, it is impossible unless the ship were refueled in space.

The Doctor listens to her pronouncements with mild amusement. She is convinced she's right due to her impeccable logic and command of facts. The Doctor tells her that logic only allows one to be wrong "with authority". The Doctor has another theory, but Zoe won't let go of her own. That rocket was driven here deliberately. She is certain of it.

The Cyber-planner reports to its agents on the Silver Carrier. The star in Messier 13 did not go nova naturally. It was engineered by the Cybermen, as were the meteorites heading directly for the Wheel. The cybermats will consume all bernalium on board the station and it will be defenceless. The plan is for the crew of the station to discover bernalium on board the Silver Carrier and transport it to the station. The next phase is now ready. A signal is sent to the cybermats on the Wheel, who respond with their own signals and move out.

Bill Duggan has learned to his horror that there are no more bernalium stocks on the Wheel. All that there was has been consumed by this "space bug". With abject sorrow, he informs Dr. Corwyn. Even if he can fix the laser in time, there is no more bernalium to run it.

Gemma is more interested in the creature that did this. He hasn't told anyone else about it yet for fear of the dressing-down he'll get, but he describes it for her and the way it corroded and ate away the centres of all the bernalium rods. He has no idea how it got on board but Gemma thinks she might. She would like to see the creature and Duggan leads her back to the power room.

Crewman Rudkin returns to the power room to find it unoccupied. However, he does spy a couple of cybermats crawling along the floor. He is horrified by them and makes a move to attack them with a hammer. The eyes on one of the creatures flash and the hammer flies from his hand. More of the creatures start to swarm into the room, coming from every corner, and they surround him.

He is trapped and blocked from reaching the door. The cybermats begin to close in. Desperate, Rudkin grabs a canister of the quick-seal plastic and starts spraying the nearest creature. He manages to coat it thoroughly, stopping it in its tracks, before another energy beam hits him and he drops the spray can.

The cybermats move in for the kill and Rudkin screams in terror.

Duggan and Dr. Corwyn hear the scream and set off at a run toward the power room.

The screams are heard in the medical bay as well. Jamie tries to go outside but he is halted by the guard. It sounded to the guard like all the devils in hell were hounding someone!

Gemma pronounces the crewman dead, but there is no evidence of how he was killed. Before she can leave to talk to the Controller, she notices the lump of plastic on the floor. What can it be?

Some time later, the plastic lump, still attached to the metal floor plate is in the hands of the Doctor. Zoe says there is no way to cut through the plastic and that was the only way it could be removed from the power room. The Doctor is sure he can find a way to get through the plastic. Zoe has explained to him about the destruction of the bernalium too and he thinks there's a connection.

The Doctor asks Jamie's opinion and he suggests that maybe Bennett was right. Perhaps there is a saboteur aboard. They are using the arrival of the rocket - and two scapegoats - to begin attacking the Wheel and making it vulnerable. The crewman was murdered to cover up their activities.

The Doctor isn't convinced of this theory and he thinks that whatever is inside the plastic lump will give them the answer. Zoe reminds him it is unbreakable and he calmly tells her they don't need to break it. They just need to see inside, a job for which a simply x-ray machine is perfect. Sometimes common sense eludes the smartest of us.

As expected, Bennett is furious at the dereliction of duty which has left the Wheel defenceless. Duggan is relieved of his duty, confined to quarters, and will be shipped back to Earth on the very next ship. Tanya is directed to take over some of Leo's duties while he takes over repair work on the laser. It should be his top priority.

Meanwhile, two men are being despatched to the Silver Carrier to search for any bernalium stocks it might have been carrying. Bennett then leaves the operations room with Gemma for a conference.

Duggan waits by the door to be conducted to his quarters. He is despondent. Tanya joins him, trying to offer sympathy but he knows it is useless. They can't even find evidence of the creature that ate the bernalium. But it doesn't really matter. With Rudkin dead, there's no justification for what he did. Duggan leaves ops, his head down.

Leo speaks quietly with Tanya. Clearly they have a relationship that goes beyond the mere professional. He apologises for having to spend so much time on the x-ray laser repair and hopes she'll understand. She has a wicked sense of humour and says she'll find someone to spend time with. He understands.

Gemma discusses the situation with Bennett. For once, she is the one being alarmist, although she couches it in very logical terms. She ties in the arrival of the Silver Carrier with the onset of the temperature and pressure losses, as well as the second above-average sized meteorite storms in one week. She thinks they're connected and she feels that the two strangers are somehow to blame, especially in light of Jamie's sabotage of the x-ray laser. Bennett tries to convince her that she's jumping to conclusions, lumping together random, unrelated events to create hysteria. However, she adds the arrival of Duggan's "space bug" and the destruction of their bernalium stocks to the situation and it looks grim to her.

Bennett begs her for some calm clear thinking. He cannot run this station with pointless hysteria running rampant. He assures her that the two men headed to the rocket will learn once and for all if there is anything wrong there.

Zoe brings the Doctor the processed x-rays of the lump of plastic found in the power room. Both the Doctor and Jamie are startled at what they see - the so-called "space bug" is really a cybermat, deadly harbinger of the Cybermen. Both of them are very grave, worrying Zoe. The Cybermen are here, and the Doctor is convinced the only place they can be is on that rocket.

Aboard the Silver Carrier, Bennett's men are finding out the truth. Laleham and Vallance space-walk to the rocket and enter through the airlock. As they explore, they hear a noise behind them. They turn and are set upon by two Cybermen. The creatures fire waves of energy at the two men. They try to resist but their minds are taken over by the Cybermen.

The Doctor has summoned Controller Bennett and Dr. Corwyn to give them the bad news about the Cybermen. However, Bennett's reaction is very odd. He seems to want to deny the reality before him. The x-ray doesn't convince him there are aliens about, even when Zoe assures him it is real. The Doctor insists that the Cybermen are real, inhuman cyborgs bent on destruction. Bennett refuses to believe this, despite the Doctor's insistence, a fact not lost on Dr. Corwyn.

On board the Silver Carrier, Laleham and Vallance assist the Cybermen in their plans to infiltrate the Wheel. The two creatures climb into an oversized crate and the humans fit a false bottom over them. They then stack boxes of bernalium rods on top.

The Doctor tries to warn Bennett that the Cybermen will try to get aboard the Wheel. They have already sent the cybermats to weaken the station's defences. Infiltration is the next logical step. Jamie joins in the alarm and it is enough to convince Gemma of the threat. Bennett, however, seems to have had all he can handle of mysterious occurrences and unexplained phenomena. He seems to blank out. There is no way anything can get inside the Wheel and too many people, Gemma included, are simply trying to spread fear and panic amongst the crew. He refuses to listen to them. He is in command and will not be contradicted. He stops abruptly in mid-torrent and leaves the room.

Gemma is stunned, as is the Doctor. He has no idea how to reason with a man like that. Gemma, taking initiative, has Zoe go and fetch Bill Duggan to see the x-ray. She knows this situation warrants further investigation. However, she agrees with Bennett about one thing: these Cybermen can't just waltz onto the station. The Doctor assures her, with grim certainty, that they will find a way.

Indeed, they are already on their way. Laleham and Vallance begin their return space walk from the rocket, towing the giant crate behind them.

Vallance calls in, requesting entry through the loading bay. Enrico is concerned as they were supposed to return via airlock 5. Tanya listens in as Vallance reports the discovery of a crate of bernalium. She contacts Bennett, just to make sure it is all right to bring the crate aboard. As if he had heard nothing the Doctor said, Bennett gives the go ahead, very pleased with the find. This only seems to confirm to him that everything is fine.

Duggan sees the x-ray and confirms that the cybermat is his "billybug". He finds it hard to believe though that this odd little creature could be capable of killing a person, however he does believe the Doctor's stern warning. If only he could have warned the crew sooner. However, even when faced with the evidence Bennett has refused to act. This worries the Doctor.

Zoe takes Duggan back to his quarters where he is still to be confined. She has more work to do calculating the trajectory of the incoming meteorites. In the hubbub over the cybermat, this impending problem has been overlooked.

The Doctor at first assumes that the cybermats were sent in to disable the x-ray laser, absolving Jamie of some of the blame for his sabotage. If he hadn't wrecked the laser, the cybermats would have put it out of action by eating the bernalium. But on further thought, there seems to be more to this plan. The Wheel has other defences, including magnetic field deflectors, and eating bernalium is not the surest way to defeat the laser. The Doctor is sure there must have been another reason the bernalium was destroyed.

Unfortunately, the Doctor is not aware of how right he is. The two crewmen arrive in the loading bay with the crate.

In the para-psychology library, Zoe is trying to record a warning message for incoming ships, to let them know about the meteorites. However, Jamie wanders in and speaks to her, ruining the recording. Jamie of course has no idea what a "recording" is nor how he ruined it. He is a bit bored and feels quite at sea in this adventure. None of what is happening makes sense to him. He's also feeling the ire of the crew for damaging the laser. Zoe, however, seems to have warmed to him, even though he still won't reveal the real reason he needed to disable the gun.

In the power room, Leo Ryan continues work on the laser. He has done three consecutive duty shifts without resting in hopes of completing repairs. All of the men working with him have been working endlessly as well and it is starting to affect them. It is actually slowing up the work. Controller Bennett arrives, along with Duggan. He has been released from confinement and is being put to work on the laser. There's no reason he can't be useful. Bennett seems unusually cheerful as he dismisses the other crewman to take a break.

The men are reluctant to go when there's work to be done, but Leo insists. They head off. Leo tells Duggan that things are going very well. The central deployment was untouched by the plastic and will not need to be repaired. That will take many long hours off the repair work. Duggan is encouraged, and glad to be able to redeem himself by assisting with the repairs. He tries to convince Leo to take a break, but he won't go. Crewman Chang arrives, having been sent along by Bennett. This tears it and Leo decides to take a break for a while. Duggan and Chang set to work.

Dr. Corwyn completes another examination of the Doctor. She calls his x-ray "extraordinary" and says that while he'll still have a headache for some time, he should suffer no permanent damage. The Doctor takes the opportunity to strike up a quiet conversation with the friendly Gemma Corwyn. He wants to know more about Controller Bennett and she seems willing to talk.

The Doctor thinks him a strange sort of man to be in charge in a place like this. Running a space station is a high-pressure job and he seems to have little tolerance for events out of the ordinary. It seems to the Doctor like there is nothing "ordinary" in a job like this. Gemma agrees, but tries to downplay Bennett's problems. She says he simply can't accept phenomena outside the laws of physics. That sounds to the Doctor like a diagnosis and Gemma agrees that it is. She admits that she has been concerned about Bennett lately. He is showing signs that he is blocking off his mind to the unexplainable. Despite the facts, he seems unable to face the truth.

Bennett walks into the operations area, seemingly in a daze of good humour. He asks Tanya if everything's in order but doesn't even wait for a response. He can see that everything is fine. Then he is gone, as abruptly as he entered.

He continues his "tour" of the Wheel, heading down several corridors mumbling to himself.

In the medical unit, the Doctor is at last getting out of bed. Gemma tries to stop him, even trying to enlist Jamie's aid in helping to stay here and rest, but he insists he must get up. There is much to do. The Cybermen are here to start their plan to colonise Earth. They must have the treasures of the planet and he must stop them.

Gemma tries to pull rank, invoking Bennett's orders that he be confined here, but both of them know that the Controller is not thinking or acting rationally at this moment. Gemma refuses to countermand the order and there's still a guard outside to stop him leaving.

Bennett continues down the corridors, smiling benevolently on everyone he sees. Everything is in order in his world. He is blocking out anything other than business as usual. He reaches the medical bay and seems pleased to see the Doctor up and about. That's as it should be. He tells Gemma, sounding like a schoolboy reporting to the headmistress, that he has done a tour and everything is running like clockwork. When she attempts to bring up the subject of the rocket, however, he blanks her out, still smiling insanely.

Bennett suggests that the Doctor find someone to give him a tour of the station, which the Doctor exploits into carte blanche to leave the medical bay. To Gemma's surprise, Bennett actually dismisses the guard and leaves the Doctor free to go. She tries to talk to the Controller but he plows over her with reports of excellent morale and situation normal. Suddenly he is tired and decides to take a rest. He tells the stunned occupants of the medical bay to "keep up the good work" and then disappears.

Duggan removes the bernalium rods from the x-ray laser. They are still intact but covered in plastic. Useless. Chang tells him about the new supply brought over from the rocket and Duggan is stunned. Things aren't nearly as bleak as he feared. He sends Chang to fetch a dozen rods as quickly as he can. With any luck, they can have the laser reassembled in a couple of hours.

Chang heads for the loading bay where the giant crate still sits. However, the crate is now empty. The boxes of bernalium sit on the floor, but the crate's other cargo is at large in the loading bay. Chang turns at a sudden noise and cannot believe his eyes - a silver robotic giant bearing down on him. He is frightened and tries to escape but there is nowhere for him to go.

As the Cyberman approaches, Chang sees Laleham and Vallance standing nearby. He begs them for help but the two controlled men do not move. The Cyberman activates a control on its chest unit and a glowing burst of energy streams out. It catches Chang full on and he screams as he dies.

At a signal from the Cybermen, Laleham and Vallance pick up Chang's body and move toward a piece of equipment in one wall.

In ops, Tanya notes an anomalous energy reading from the loading bay - the waste incinerator. No one has clearance to use it and everyone is suspicious, but they decide not to check just now. Tanya notes the unauthorised power use into the log where it will be investigated later. Someone will be punished; Leo is sure of that.

Duggan is surprised to see not Chang but Laleham and Vallance return with the bernalium rods. Laleham explains that Chang cut his hand opening one of the boxes and had to go to the medical bay. Duggan accepts this story, not noting the flat, emotionless tone in Laleham's voice. All that matters to Duggan is that these new rods are the right length. Both Vallance and Laleham are certain that they are, strangely certain.

While Duggan works, the two men state repeatedly that it is imperative the laser be fixed in order to stop the incoming meteorites. Duggan appreciates the sentiment but would appreciate some help - or some quiet - from them instead. He is glad to find that the rods are the right size. He should be able to complete repairs and have the laser operational in just six or seven hours. Close, but ahead of the meteorites.

Duggan returns to work, whistling happily. There is silence from the crewmen. However, when he turns, Duggan finds out why. They have been joined by a Cyberman. Like Chang before him, Duggan cannot believe what he is seeing. The silver giant is terrifying. It releases a mind-controlling ray aimed at Duggan. He screams when it hits him and is soon taken over, joining Laleham and Vallance in service to the Cybermen.

The Cyberman repeats its insistence that the Wheel must be protected from the meteorites. It will complete the repairs on the laser whilst Duggan is sent to ops on a mission...

Zoe approaches Dr. Corwyn, a worried look on her face. She reports that she's done some new calculations on the incoming meteorites and the figures indicate that the storm is more critical than she had initially thought. However, when she reported her figures to the Controller, he ordered her to forget them! He told her everything was perfectly normal and she knows full well it is not.

Gemma receives this news sadly. Bennett is ill and clearly getting worse. Zoe responds mildly that the timing is inconvenient and Gemma is disgusted. She accuses Zoe of lacking any emotions, the second time someone has done so today. Gemma relents, knowing that her concern made her respond more harshly than she'd intended to. She tells Zoe that it is her training as a para-psychologist that made her so emotionless and says it doesn't really matter. However, Zoe is quite concerned about it. She doesn't want to be thought of as a freak, some emotionless automaton only good for reeling out facts and figures as needed. She doesn't want to lose touch with her emotions, despite the value of her work.

Gemma smiles at her and assures her this is not the case. She has not been completely brain-washed by her teachers just yet. Relieved, Zoe is ready to tell her about the new calculations.

The Doctor is being shown round operations by Tanya Lernov. When Leo takes her away for a moment, the Doctor and Jamie have a chance to speak quietly. Jamie reminds him of the mercury they need for the TARDIS. The Doctor assures him he hasn't forgotten. Their attention is drawn by a hushed conference going on on the other side of the room. Zoe and Gemma have joined Leo and Tanya and they talk animatedly. The Doctor joins them quickly to hear about Zoe's new calculations. She has determined that the meteorites are heading toward the station faster than expected. The Doctor is concerned that the laser won't be repaired in time, but Zoe is more worried about the Controller's strange response to the news.

The Doctor brushes this aside to concentrate on the laser gun. Even if it's been repaired, there is still no bernalium to power it. Zoe reports the finding of the crate and its return from the Silver Carrier, to which the Doctor responds in horror. He is certain that the Cybermen go onto the station hidden in that crate. The two men who went over must have been hypnotised and are now obeying their orders. That was the plan all along!

Gemma doubts that the men were taken over. All space-based crew are protected against mind-control by drugs. However, she must admit that not every part of the brain has been blocked. The Doctor believes that the Cybermen are able to bypass the drug easily. Gemma tells him that there is a circuit implanted in each crewmember to monitor any adverse affects on their minds and would register any kind of mind-control. The Doctor insists that these circuits be checked.

Tanya says this is easily done, but it would require power activated for the entire defence network. It would take a lot of their precious power to do so. Seeing the determination in the Doctor's face, Dr. Corwyn authorises the extra power usage. As the scanning equipment is powered up, Bill Duggan enters the operations room unnoticed.

The Doctor huddles with the others to check the readings. He decides to concentrate on this room first, hoping to find that no one here is affected.

Jamie and Zoe notice Duggan walking slowly and deliberately toward one of the control panels. They think it strange as he's supposed to be confined to quarters. Zoe tries to talk to him but he moves on, ignoring her completely.

The Silenski circuit scan shows that the Doctor was right. Someone in this very room is under mind control. They work feverishly to try and pin it down to an individual, ignoring what is going on right behind them. By the time they work it out, Duggan has reached the communications panel and raised the spanner that he has concealed in one hand.

The Doctor shouts out a warning as he attacks the panel. There is a fierce struggle but Duggan is able to break loose and batter the communications console. The entire thing erupts in smoke and flames. Leo grabs a gun and fires at Duggan. There is a scream and he falls to the ground, dead.

The Doctor moves into action. He reports unequivocally that the Cybermen are on board the Wheel. They took over Duggan's mind in order to sabotage the communications equipment and cut the Wheel off from Earth. He urges Gemma to use stronger methods to protect the crew from mental control. A transistor and a metal plate taped to the back of a person's neck will absorb the signal and keep the crew safe. Leo and Tanya volunteer to organise that.

The Doctor grabs Jamie and starts to head out. He tells his companion that they are "going hunting".

Zoe, left on her own, tries to find some way to help. There is some resistance at first. Clearly Zoe is seen as valuable only for her mental capacity. However, Tanya relents and accepts her assistance.

The Doctor and Jamie head straight for the loading bay, where the crate was brought in. The place is dark and silent. The crate is there, as are the boxes of bernalium. It is clear, though, that there was something else in the crate.

The Doctor and Jamie hold their breath and stay completely still in the gloom of the loading bay. There is no place to hide. If the Cyberman sees them, they are done for. Luckily for them, the creature is engrossed in its task and does not deviate. It picks up a box of bernalium rods and carries it out of the loading bay.

When it is gone, the Doctor and Jamie can finally breathe again. The Doctor is puzzled over one aspect of the Cybermen's plan. It appears that by disabling the laser, they planned for the Wheel to be destroyed in the meteorite storm. But now that they're on board, they themselves will be in danger. Clearly, destroying the Wheel is not part of the plan.

The Doctor puts this aside for the moment and turns his mind to protecting the crew of the Wheel. He is already several jumps ahead. He knows that the Cybermen don't need air to breathe, and everyone on board this station does. That is their greatest vulnerability and he is certain the Cybermen will exploit it. He activates the communications unit and calls to the operations room.

The Doctor orders all the airlock doors sealed to prevent them being tampered with. Leo and Tanya are willing to comply, even though they don't completely understand. They simply seem to trust the Doctor. Suddenly the Doctor breaks off as Jamie announces seeing some movement in a corner.

The line is kept open, but the crew in ops can't see what is happening. Gemma considers the Doctor's request and agrees to it. Leo seals the airlocks. Gemma doesn't really know why she trusts the Doctor, but she does. Besides, closing the airlocks is only common sense anyway.

Jamie and the Doctor search the gloomy hold for sign of the movement. It is not long in coming. A cybermat! The Doctor quickly returns to the communications unit and asks for an audio-frequency to be hooked to the communications link right away. He begs them not to ask questions and not to delay. They have very little time before the cybermat will home in on their brain waves and make a move to destroy them.

The crew in ops does as he says as quickly as they can.

More of the creatures begin scuttling from the darkness, all of them aiming for the Doctor and Jamie. They are trapped with nowhere to run. He begs the crew to move faster.

Gemma echoes the sentiment as Enrico works to connect the circuit. At last he is finished and the power is switched on. A high-pitched oscillating whine pours through the speakers and floods the loading bay. The Doctor and Jamie cringe as it assaults their ears, but it has the intended effect on the cybermats.

The little creatures begin gliding erratically along the floor, seemingly lost for bearings. Their own noises become distorted in the face of the all-pervading sound waves. They lurch out of control and eventually explode. They are all completely destroyed.

Gemma orders the power turned off and the terrible sound wave fades away. The Doctor and Jamie are very relieved. They are headed to ops shortly, but they take a moment to show Gemma what it was she saved them from. The metallic creatures repulses them all.

Meanwhile, news of the destruction of the cybermats reaches the Cybermen. They open a channel to the Cyber-planner.

Tanya monitors yet another anomalous power reading on the grid. This time it's from the power room. It is not authorised and seems to be somehow outside of the station's main power.

The Cyberman reports to the Cyber-planner the destruction of all cybermats. High-current phase contrast was used to destroy them, indicating that someone on board the Wheel has knowledge of the Cybermen and their creatures. There is some good news, though. The x-ray laser is repaired and operational, and communications with Earth have been cut off. Now it is on to phase six of the plan - to take over the station completely.

Enrico and Tanya survey the damage Duggan did to the communications console. It is not complete, but enough to make it impossible for them to call to Earth for help. However, it is still two hours before their next scheduled check-in. No one will miss them until then. Tanya is also worried about the impending meteorite storms and wants to keep track of it, even though they have no means of fighting it. She just wants to stay informed.

Leo is concerned as he cannot seem to raise any section of the Wheel. No one responds to his calls. They wonder what can be done, but prefer not to bother Dr. Corwyn with the news just yet. She has her hands full at the moment.

Controller Bennett is in ops now and Gemma is trying to get through to him about the dire situation they face. She shoves one of the dead cybermats right under his nose to get him to try and face reality. He simply says it's not true and clams up. Complete withdrawal from reality. The Doctor corrects her, saying it's not a complete withdrawal. But it is near catatonia. He might be shocked back to normal with an ECT machine, but it's not worth the time right now.

Gemma says that she's thrown up a magnetic force field around the control section and warned the crew what's going on, but that seems to be all she can do. The Doctor insists that she must take command from Bennett, but she is hopeless. They are invaded, cut off, and in the path of giant meteorites. There is nothing that she could do, even if she did take over. They have no defences.

Jamie discusses the situation with Zoe and it seems pretty hopeless to them. Jamie does wish that Dr. Corwyn would just take command but Zoe doesn't know what she could even do. Jamie gloats over Zoe's lack of a know-it-all comeback, chiding her for her closed-minded genius.

Zoe responds to this more strongly than he'd expected. She is feeling even more hopeless than everyone else because she feels useless. She has been trained to calculate and react logically, but that training doesn't serve her very well in an emergency like this. She can actually empathise with Bennett, being faced with a reality for which she is ill-prepared. But instead of shutting down, she seems to be fighting back and trying to find an answer. What will she do if by some miracle they survive this mess. It won't be because of anything she's done and she will still face a life of blind reliance on facts and logic.

Jamie doesn't know what to say to all of this. It is all beyond him.

Meanwhile, Leo has continued to try and raise any section of the station. But the Cybermen are way ahead of him. Dead bodies litter the corridors of the Wheel.

In the power room, crewman Flannigan arrives to help with work on the laser. He is about to answer the bleeping communicator when he spots Laleham and Vallance. It's not his job to answer; they should do it. Vallance ignores him. The two men give him vague and stilted answers to his questions about the laser repair and he begins to get peeved. When the communicator bleeps again, he turns to answer.

Laleham and Vallance move to block him, Vallance producing a gun. Confused and angered, Flannigan lashes out and knocks the gun away. A fight ensues. With their ungainly movements, Flannigan could easily overpower them, but there are two men against him. Laleham grabs him around the neck, knocking loose the transistor attached there to protect him. They struggle whilst Vallance regains his gun. He fires, but hits Laleham instead. He is killed instantly.

Flannigan is ready to fight Vallance, gun and all, but there is no need. A Cyberman has arrived and it uses its hypnotising ray to subdue Flannigan. He and Vallance face their master obediently. The Cyberman is concerned over the force field protecting the control area. Vallance reports that it can only be controlled from ops and cannot be disengaged. They must think of something else.

The Cyberman formulates a plan whilst Vallance and Flannigan dispose of Laleham's body.

In ops, Zoe tends to Bennett, feeding him some water. Her emotional side is not completely dormant after all.

The Doctor has learned that no one is responding to calls in the station and is not surprised. The Cyberman have clearly been busy. He also learns that not everyone has been fitted with the transistors on their necks to protect them against mind control. That must be the first priority.

Leo calls out and draws everyone to the control centre. They now have a radar contact with the approaching meteorites. It is even bigger than they thought and coming straight for the Wheel. They each weigh 200 tons or more. The anti-matter field projectors are not going to deflect them. Without the x-ray laser, they're finished. The storm is less than a million miles away now, closing fast.

Suddenly the communicator bleeps. It is Flannigan, calling from the power room. He reports completion of the work on the laser. It is even powered up. Leo is so relieved that he doesn't notice the dull and lifeless voice. He asks where Flannigan has been and buys his lame answer. All that matters is that the laser is operational and ready for testing immediately.

Outside, the great barrel of the laser moves into position for a test. Enrico is worried that they don't have time for a test. The meteorites are moving too fast. They are down to 680,000 miles already. Leo says they must have the test. They can't afford for anything to go wrong. The gun is only really effective at 50,000 miles so they'll only get one shot at each meteorite.

Leo and Tanya power up for the test, monitoring every reaction. They fire the gun and it works perfectly. Leo breathes a sigh of relief. They might just stand a chance of survival.

The meteorites continue their inexorable journey, now down to just 260,000 miles out. Leo just has time for two more quick tests of the laser's power. Satisfied that all is well, he is ready for them to come. Just in time.

The Doctor puzzles over all of this and comes up with a theory. The Cybermen have actually engineered this entire situation. They blew up the star to deliberately hurl the meteorites at the Wheel. Not to destroy it but to make its use imperative. Then they used the cybermats to destroy the bernalium stocks so that they'd have to go to the rocket and get some more. It was the only way in which the Cybermen could infiltrate the Wheel unseen - via that crate. They never intended to destroy the station. In fact, he is certain that the Cybermen themselves repaired the x-ray laser in order to save it. They are planning to use the Wheel as a launching point for an invasion of Earth! The creatures are desperate to plunder the mineral wealth of Earth and this is where they'll start.

Gemma is pleased to learn all of this, but what she really wants to know is what they can do to stop the Cybermen. Thinking, the Doctor remembers the time vector generator which he removed from the TARDIS. He turns to Jamie to find out where it is, but Jamie says the Doctor should have it. He put it in the Doctor's pocket just before the crewmembers can to bring them both from the rocket to the Wheel. Checking his pockets, the Doctor finds he does not have it. Somehow it must have slipped out while he was being moved.

Jamie wonders what all this is about but the Doctor will only tell him that the device is very important. Someone will have to go to the rocket to fetch the time vector generator. That someone is Jamie! Not interested in another space walk, Jamie resists. But the Doctor is far too busy here to go and Jamie is the only other person who knows what it looks like. Someone from the crew will go with him, but it must be him to lead the way.

With no other choice, Jamie agrees.

In the oxygen supply room, a Cyberman reports to the Cyber-planner. The x-ray laser is operational and will protect the station from the incoming meteorites. However, phase six is delayed due to the force field around the control area. The station cannot be taken over. They must initiate plan three instead.

The Cyberman obeys the order and recruits Vallance to help.

Gemma has chosen Zoe to go with Jamie. He is a bit nervous to have this very small, very brainy girl to be his back up on a dangerous trek. However, Gemma assures him she is fully qualified and will do everything she can to help him. They head off to the nearest airlock.

Leo has learned of the Doctor's plan and is furious. He cannot understand how Gemma could have agreed to it, nor how the Doctor could have suggested it in the first place. Quite aside from the normal dangers of space walking, there is the small issue of a giant meteorite storm and x-ray laser fire which will be all around them. This is an incredible risk they are taking.

The Doctor insists that Zoe calculated the risk and chose to go herself, but this does not placate Leo. He is still furious. There's also the small problem of Cybermen lurking about the Wheel. What if Gemma were to run in to one of them? He angrily orders the Doctor not to do anything more himself and returns to the control console to prepare for the attack on the meteorites.

Outside the air lock, very near to the oxygen supply room, Gemma, Jamie, and Zoe find a dead crewman. Another pointless victim of the Cybermen. They must press on. Zoe and Jamie enter the airlock to suit up for their walk. Gemma is left alone to wait, to make sure they get out all right.

Once they are safely out, Gemma calls in to ops to report. The Doctor takes the report as the others are far too occupied in their task.

Outside, the meteorites speed toward the station on a collision course.

Gemma starts to move off but she hears a noise and hides. Vallance with his Cyberman master return to the oxygen supply room. Vallance carries a small box. Gemma follows them to the door and watches as they work.

The box contains a series of capsules. They are to be placed in the air supply for each section of the Wheel. They will turn the oxygen into pure ozone, killing all the humans.

Leo orders the first firing and they are successful. Several meteorites explode into fragments. Firing continues, but Enrico is very nervous. He fears that there are too many of them coming in too fast for them to destroy them all. Leo tells him to shut up and keep firing!

Gemma reaches the communicator and calls back to ops. The Doctor answers and she tells him about the plan to poison the air supply. She tells him to get Leo to switch to sectional air supply immediately.

The Doctor listens to her, but his gaze is drawn to the scene over her shoulder. A Cyberman appears in the frame behind her. She does not see it at first but the Doctor shouts out a warning, urging her to run. She does so, leaving the communicator on while she tries to get past the giant silver creature. But she is far too late. It fires and she dies.

The Doctor is forced to watch, helpless. He calls out to her in anguish as the rest of her crewmates work desperately to save the station from the incoming meteorites.

Out in space, Jamie and Zoe are in between the Wheel and the rocket. Their progress is slow. They have been aware of the firing but have not seen the meteorites yet. They are too far away.

Suddenly the darkness of space lights up all around Jamie and Zoe as the x-ray laser is fired at the meteorites. The giant rocks explode, sending fragments of dust and rock flying all around them. Jamie and Zoe are tossed about in space, grabbing each others' hands to try and keep from flying away.

The blasts are successful in stopping the meteorites, but the Doctor tries to determine if Jamie and Zoe are all right in the midst of it all. Tanya tries to get Leo to stop firing for a moment but he refuses. The Doctor has put them in this danger so they'll have to take their chances. The only hope for the Wheel is total destruction of the meteorites. The firing continues. The Doctor pins his hopes on Zoe's calculation of the risk. He can only hope that she was right.

Jamie and Zoe are buffeted by the shock waves but are otherwise unharmed. The latest blast cause them to lose their grips on each other and they drift apart.

A few moments later, there is exhausted calm in the operations room. The radar is clear. The largest of the meteorites have been destroyed and the rest are being deflected by the station's force field. Leo and Enrico are very pleased with their success. They will remain on stand-by for any smaller formations following on but the station is out of danger now.

The Doctor asks again about Jamie and Zoe but the video screen shows no sign of them. This brings up Leo's ire once again and he chastises the Doctor for sending Jamie and Zoe out into that minefield. Anything could have happened to them out there. The Doctor tells him defensively that it was a risk that had to be taken. They could save everyone on board this station if they succeed in retrieving the time vector generator. With it, he is sure he can defeat the Cybermen.

However, there is a more pressing problem. The Doctor tells him of the plan to poison the station's air supply and that Gemma said Leo must switch to sectional air supply immediately. Leo wishes to speak to Gemma and the Doctor must sadly report that she is dead. She sacrificed her life to warn them of the danger. On the communication screen, her body can be seen just outside the oxygen supply room door. All of the operations crew are saddened by this tragedy.

Enrico reports a second wave of meteorites and Leo must tear himself away from the screen. It must be dealt with. Unnoticed by anyone, Controller Jarvis Bennett has risen from his near-catatonia in the corner. It isn't the meteorites or the activity or the threat posed to Jamie and Zoe that has roused him. It is the image of his friend Gemma Corwyn on the monitor that has broken through his mental haze. He approaches the screen and gazes at it for a long time, saying nothing. With an unreadable look on his face, Jarvis leaves ops.

Leo and Enrico are ready to fire again at the new swarm, but Leo is worried about the laser. The bernalium rods must be nearly burnt out and they'll be unable to get to the power room to replace them. As expected, the power begins dropping as they fire the laser again. Desperately, Leo orders the anti-matter projectors activated. Hopefully, these meteorites are small enough to be deflected without needing to be destroyed. To his great joy, it works. They are deflected and the station is once again safe.

The Doctor rejoices with them, but his attention is diverted when he notices that Bennett is no longer here.

He walks the corridors of his station, bereft and single-minded. He notices nothing.

Leo and Tanya adjust the communications system to try and find Jarvis. At last they spot him in a corridor and call to him. He responds, refusing to come back. He is out to find Gemma's killers and will not be dissuaded. He notes blankly that he lifted the force field in order to leave. Leo had better put it back.

Leo ignores this and starts to leave ops to fetch him back, but he is far too late. The Doctor sees the Cyberman on the screen. Jarvis sees it too and turns. The massive and horrible creature does not faze him. He moves forward, a look of determination on his face.

The two meet in the midst of the corridor, but Jarvis is far outmatched. The Cyberman grabs him by the throat and strangles him. It then raises the body above its head and flings him to the floor. The Doctor, Leo, and Tanya watch on the monitor as the Cyberman activates its chest unit and destroys Jarvis once and for all. Horrified, Tanya begs the Doctor to turn the monitor off.

In the control room of the Silver Carrier, Zoe slumps in a chair and removes her space helmet. She is breathing heavily. They have been through a lot. Jamie brings her a drink from the food machine and they rest for a moment, getting their strength back after the dangerous crossing. Neither of them thought they'd make it and they are quite worse for wear.

However, they know how important their mission is and set about trying to find the precious time vector generator.

With the meteorites destroyed, the Cybermen continue with their plans. The ozone capsules are inserted into the air supply and activated. However, Vallance reports a problem. The emergency oxygen supply has been activated and the capsules are useless. What's more, the controls for the emergency supply are in the control area, inside the force field.

The Cyberman reports this to the Cyber-planner via a small communications box. Their plans have somehow been anticipated and thwarted. The Cyber-planner realises that someone on board the Wheel has knowledge of the Cybermen and their methods. Identification of this person is essential.

Zoe has returned to the control room of the rocket and is fiddling with the communications system. Jamie arrives having found the time vector generator but Zoe is engrossed in the screen. She has managed to break into the Cybermen's communication frequency and can overhear the conversation with the Cyber-planner.

A mental beam is sent from the Cyberman to Vallance, who is then set the task of mentally picturing all of the individuals on the Wheel. On the communications channel, a picture of each person forms as Vallance identifies them. Tanya Lernov, Leo Ryan, and Jarvis Bennett are all pictured. The Cyber-planner does not recognise any of them.

Zoe and Jamie watch all of this from the rocket, wondering what is going on. Zoe's picture comes up. She too is unknown to the Cybermen.

However, the next picture is that of the Doctor. Vallance knows he is on the Wheel but knows he is not a crewman. He is known only as the Doctor. The Cyber-planner takes this all in.

The Doctor and Leo, now acting Controller of the station, argue over the reason for the invasion of the Wheel. The Doctor feels it must be for a greater purpose. The Wheel itself is a very small target for this elaborate plan. The answer comes via the radar. There is a contact, a large one, approaching the Wheel. It is not a meteorite but a very large space ship. The Cybermen.

Leo is anxious to try and contact Earth, to at least let them know what is happening, but the radio is still out of action. Enrico thinks he could fix it with some new transistors, but those are in the power room and it would be far too dangerous to go. But they must. Somehow, one of them must get through.

The Cyber-planner returns a positive identification of the Doctor. He is known and recorded as an enemy of the Cybermen. He must be lured outside the force field and destroyed.

Jamie and Zoe overhear this and Jamie is quick to react. They must get back to the Wheel and warn him immediately.

Tanya and Leo examine a map of the Wheel, trying to find a safe route to the power room. It is not easy. All that appears to be open is the emergency air tunnels.

Suddenly the communications system activates and crewman Flannigan appears. He puts in play the Cybermen's plan. He tells Leo that he has a group of Cybermen trapped in the workshop. When Leo asks about the way to the power room, Flannigan says it is clear. Leo cannot tell that Flannigan is taken over and reveals their need to get to the power room. Flannigan says he will help to keep the corridors clear. The Doctor listens to all of this and volunteers to go for the spares. He agrees to meet Flannigan in corridor six.

However, once the communications link is closed, the Doctor changes tack completely. He was not fooled for a moment by Flannigan. This is part of a plan to trap him. He is certain that Flannigan will not keep the appointment and will instead try to get inside the force field as the Doctor leaves. He tells Leo and Tanya to grab him when he does so and check the metal plate at the back of his neck. He is certain that it has been dislodged. The Doctor reverts to the original plan to go through the air tunnels. He will brook no delay and grabs the map, issuing orders all the way. Then he is gone.

Flannigan reports to the Cybermen and receives the order the Doctor expected. He is to get through the force field and go to operations. His task is to destroy the force field so the Cybermen can take control of the Wheel.

Jamie and Zoe, meanwhile, undertake another space walk to return to the Wheel. This is one is much easier and quicker. No one is shooting meteorites right on top of them!

The Doctor emerges from the air tunnel into the power room. Looking around, he finds not the spares but a bottle of mercury. Remembering he needs it for the TARDIS, he pockets the container and continues looking around. He finds the spares he needs but is also drawn by a generating machine on another bench. The Doctor has an idea...

Jamie and Zoe emerge from the airlock and are startled to see Dr. Corwyn's body on the floor. Clearly, much has happened since they left. The two young people hurry off to find the Doctor. They run straight into Flannigan, nearly frightening themselves to death. He befriends them, and even they can't tell that he has been taken over. Foolishly, they follow him.

Vallance and a Cyberman have been waiting for the Doctor in corridor six. It is clear that he on to them and is not coming this way. Vallance remembers the emergency air tunnels and knows that the Doctor could reach the power room that way. The Cyberman orders Vallance to show him.

Flannigan leads Jamie and Zoe to the operations room but is immediately jumped by Leo and Enrico. They wrestle him to the ground and attach a new metal plate and transistor to his neck. Flannigan cries out as he is freed of the Cyber-influence and collapses. Zoe can hardly believe that Flannigan was under mental control. She and Jamie are both lucky to still be alive.

Jamie looks around for the Doctor but learns to his dismay that he is gone. The communications system activates. It is the Doctor. He announces he has the needed spares and is pleased to see Jamie and Zoe alive and well. Jamie tells him that the Cybermen know he is here and that they are working on a plan to trap him. But there is no time for that now. When Jamie shows him the time vector generator, the Doctor tells him he must make his way to the power room via the air tunnels. Time is of the essence.

Suddenly the Doctor breaks off, a look of worry on his face. He says, cryptically, that he has "company" and switches off the link. Jamie knows all too well what this means. Cybermen.

Two of the creatures have entered the power room. They stand motionless. The Doctor realised long ago that the Cybermen would get on to him sooner or later. Now they have caught up with him. He also knows that they have orders to destroy him. Before they do, he wants to know why they are invading the Wheel. He learns that Duggan was only ordered to destroy the station's transmitting equipment, not its receivers. Invasion of Earth is their plan, and they need a radio beam from there to home in on. He deduces this on his own, prompting the Cybermen to repeat that they must destroy him. He knows their ways too well.

The Doctor invites the creatures in, but as soon as the first one steps forward, he activates a jury-rigged electrical force field. It has been cobbled together from spares in the room, but it is entirely effective. The Cyberman twitches as power floods through it, then collapses in a heap on the floor. The second Cyberman tries to fire its weapon at the Doctor, but the force field stops it. The Doctor is safe.

The Cyberman retreats from the room, promising that the Doctor will be destroyed one way or another. More Cybermen are on their way.

Once he is sure the creature is gone, the Doctor switches off the force field. At the same moment, the grille to the air tunnel opens. Jamie and Flannigan emerge. The Doctor is delighted to see Jamie again, but is concerned that Flannigan might still be under the influence of the Cybermen. It is soon clear that he is not. Flannigan complains of a bad headache and promises to make the Cybermen pay for it.

There is little time to talk. The Doctor takes the time vector generator and begins connecting it into the circuitry of the x-ray laser. With any luck, he'll be able to boost the power of the weapon and destroy the Cyberman spaceship. However, there is still the matter of impending reinforcements. He is certain that they'll try to enter through the loading bay and he wants Jamie and Flannigan to hold them off.

Flannigan takes a canister of the quick seal plastic with which to attack the remaining Cyberman should they encounter it, and the Doctor gives him a metal plate and transistor to deprogramme Vallance if possible. Jamie has only a moment to tell the Doctor to call Leo before dashing off with Flannigan.

In ops, the Cyberman spaceship is clearly on the radar, closing in. The Doctor calls in and tells Leo what he is doing. He tells Leo to hurry and align the laser with the incoming ship and await his signal to fire. There is no time to lose.

Jamie and Flannigan, now outfitted in space suits, arrive in the loading bay. The Doctor was right; this is where the Cybermen will arrive. Vallance is there, along with his Cyberman master. Vallance pretends to be under Cyber-influence and says that Jamie is his prisoner. The Cyberman doesn't seem to mind, although Vallance seems to be suspicious.

The Doctor struggles to connect the generator, an alien piece of equipment, into the x-ray laser. It is not easy. It is made no easier by Leo Ryan badgering the Doctor on video, urging him to hurry!

But time is of the essence. A group of Cybermen space walk toward the Wheel through empty space. They are unaffected by the lack of air, the freezing temperatures, or the lack of gravity. They walk as if on dry ground, inexorably toward the loading bay door.

The Cyberman inside the bay, moves to open the door for its comrades. As it does so, Jamie and Flannigan make their move against Vallance. They both grab him and struggle to subdue him. At last, Jamie succeeds in attaching the metal plate to the back of his space helmet. The Cyber signal is absorbed and Flannigan cries out as he is released from control.

The Cyberman hears the struggle and moves toward Flannigan. He reacts quickly, emptying the can of plastic directly into the Cyberman's chest unit. The gamble works and the creature begins to stagger, ignoring the humans. It has but one task which it must complete - opening the loading bay doors. It reaches the wall and falls against the control panel, managing to activate the door control as it slumps to the floor.

The Cybermen in space are now mere feet away from the door. Jamie and Flannigan struggle against the outrush of air to reach the door controls. Flannigan succeeds and activates the control. The doors start to slide shut, but very very slowly. The Cybermen are nearly upon it.

In fact, the lead Cyberman reaches the door before it closes and wedges itself inside, fighting to keep it open.

The Doctor reports to Leo that he is now ready. The time vector generator has been installed and the x-ray laser's power has been boosted. Time to fire.

The Cyberman spaceship is nearly upon the Wheel, and Leo knows they will have only one shot. He fires, and he is right on the money. The ship explodes in space, killing all the Cybermen on board.

However, there are still Cybermen at the loading bay, trying to get in. Amazingly, the lead Cyberman has managed to push the doors open a bit. It looks as though it may succeed in getting in.

But the crew in the operations room hasn't forgotten about the loading bay. They activate the neutron force-field to repel the invaders. Jamie and Flannigan must hold on for their lives as the mighty field is activated. The Cybermen are flung away from the Wheel and off into space.

The loading bay doors close and the air pressure returns. Vallance, now recovered, operates the oxygen controls and soon all three men can open their space helmets and breathe the air again. They have succeeded. The Wheel is safe.

Some time later, things are very much back to normal. Communications with Earth have been re-established and it is time to give a report. Only Zoe is not there. Tanya reports that she has gone to the rocket with Jamie and the Doctor, to see them off. Acting Controller Ryan commences his report about an alien invasion. As he speaks, he holds Tanya's hand. They have survived together through tragedy.

On board the Silver Carrier, Jamie is ready to leave. Zoe cannot believe he and the Doctor are just going to disappear into thin air. She has heard the Doctor's explanation of the TARDIS and she doesn't believe a word of it. Jamie's method of explanation is simply to tell her they are from "two different worlds". He's sad to say goodbye to this strange bright girl, but it's time to go. The Doctor calls out to him and he hurries off, telling Zoe that they won't forget her. A look of determination creases her face as he goes.

Inside the TARDIS, all is back to normal. The inner dimensions are as they have always been and the Doctor is slowly refilling the console with much-needed mercury. There's even a bit to spare. He hits the main switch and the time rotor in the centre of the console lights up and the ship's familiar hum issues from all around. The Doctor is very pleased.

Jamie arrives, glad to find everything all right. He is anxious to be off. The Doctor is too, but there is another little matter to settle first. He has noticed a movement behind Jamie and watches as the lid of an old wooden chest settles shut. The Doctor goes over to it, knocks, and then flings open the lid. It is Zoe, stowing away!

She says determinedly that she wants to go with them. Jamie says it's impossible but the Doctor is not so closed-minded. It is something, he says, that they will have to discuss. Once he tells her of the dangers she will face, she might change her mind. The tough girl is resolute.

The Doctor goes to a hatch in the wall and removes a small headset with wires connected to it. He places it on his head and directs Zoe to the scanner screen. He's going to use thought patterns to show Zoe what she might encounter on their travels, and he plans to weave them into a complete tale. A tale of the Daleks.

Zoe has never heard of the creatures and she stares raptly at the scanner. A scene appears of the Doctor's most recent adventure with the Daleks, when they stole the TARDIS in 1966 in order to spirit the Doctor and Jamie back in time and gain their assistance distilling the evil "Dalek factor". It seems so long ago, yet the pictures are as clear as if they were happening at this very moment.

In a secret room, a Dalek confronts a man called Kennedy. He, too, has never seen a Dalek before. In its grating metallic voice, the Dalek orders Kennedy to identify himself. He is too frightened to speak. As soon as he is able, he makes a run for the door. He does not make it. The Dalek fires and he falls to the ground. Dead.