Jamie has found a handhold along one wall of the console room while the Doctor and Victoria cling to the base of the console itself. The TARDIS bucks and pitches as it flies through time with its doors wide open. A wild roaring fills the room.

The Doctor calls to Jamie, the only one in a position to help. He's got to get to the control panel and close the doors. Jamie manoeuvres himself to a better position with which to fall against the console. Trouble is, if he misses, he'll fly right out the door. The Doctor helps Victoria hold on while Jamie lets go and falls against the console.

He still has to get round to the side where the door control is and that is much more tricky. He reaches as far as he can but cannot touch the control. He decides to give it one last try, letting go and falling forward, lunging for the switch as he does so.

Jamie falls to the floor, heading for the doors, but suddenly they begin to close. The floor levels out and the wild bucking stops. They are safe. Jamie has done it!

The Doctor stands and helps his companions up. They all assess their damage. He explains that the evil dictator Salamander, the Doctor's exact double, started the TARDIS without first closing the doors. He really had no idea what he was doing but ended up being sucked out into the time vortex. There he will remain.

The Doctor pulls himself together and turns to the controls. Where should they go next. Jamie is more than willing to stay where they are for now, at least until they get their breath back. Besides, the Doctor can't control the ship anyway. They all know that. A bit put out by that remark, the Doctor activates the controls. They are shortly in smooth flight.

However, even the Doctor himself must admit that he doesn't know where they'll end up.

Elsewhere, on Earth, a new adventure is already beginning. A greying, bearded old man stands in the eerie, candle-lit house of one Julius Silverstein. Silverstein is a collector of rare and exotic artefacts and his house is something of a museum. One exhibit in particular rivets the attention of the old man - that of a Yeti. But this is not the Abominable Snowman of myth and legend. It is a robotic creature brought back from the mountains of Tibet many years ago and now residing in this collection. The creature was the plaything of an unearthly entity known as the Great Intelligence in its attempt to gain corporeal form on Earth. But the old man knows all of this. He witnessed it all firsthand. His name is Professor Travers,

Mr. Silverstein answers his front door, a great agitation in his voice. The newcomer is a young woman - Professor Travers' daughter Anne. She is here to take him home. Silverstein will be only too glad to rid himself of the troublesome Travers, calling him an old fool.

Anne tries to be as gentle as she can with her father, treating almost like a child, but chiding him for forgetting to pick her up at the airport. He had cabled her that he was in trouble and she came half way round the world to help, only for him to leave her waiting at the airport.

Travers cares little for all of this. The Yeti is what concerns him. He has been trying to convince Silverstein to return the Yeti to him. It was Travers who brought it back from Tibet but then gave it to Silverstein for his collection. Now Travers comes here trying to frighten him into returning it. Silverstein will have none of it. None of it!

Anne tries to reason with her father, reminding him that the Yeti robot is dormant without a control sphere in its chest. To her horror, Travers tells her that he has succeeded in reactivating one of the spheres. Now it has disappeared. He appeals to Silverstein once again - in a very rough and ungracious way - to return the Yeti before it becomes active again. Silverstein accuses him of trying to swindle him, even though Travers offers to pay for it. Silverstein refuses. The robot is unique and priceless. He will not part with it.

Anne again tries to soothe her father, suggesting that perhaps he just mislaid the sphere. The old man, brilliant yet a bit dotty with the years, protests but she eventually convinces him to go with her. They can talk quietly about it over dinner and then go home to look for the sphere. Travers does go, but he reminds Silverstein that he warned him. Whatever happens now is his own fault.

Silverstein badgers the old man all the way out, then once quiet returns to his house, he goes about putting out all of the candles.

Outside, a strange sight appears in the window. It is a silvery sphere, hovering in the air, bleeping to itself. A Yeti control sphere. Travers was right -- it is alive again. The sphere hovers there for a moment and then propels itself through the window with a crash. Silverstein starts at the noise, but believes that it's Travers trying to frighten him. He calls out but there is no response.

His searches take him back into the room where the Yeti is kept. Behind him, the Yeti comes to life, changing form from bear-like to more streamlined and ferocious. It's large eyes glow. Silverstein turns just in time to see the creature raise its massive arm. He screams as the claws slash down at him.

On board the TARDIS, Jamie and the Doctor enjoy a snack... and engage in a small argument. Jamie insists that a small light on the console had been flashing, indicating a landing. However, the Doctor insists they are still in flight. The argument is petty but irresolvable.

Victoria enters and shows off a new dress she found in the wardrobe. It is very short but she thinks it quite "sophisticated". The Doctor agrees but is soon back in the argument with Jamie.

Victoria asks innocently why the light is flashing. The Doctor comes round the console to investigate and finds that she is right. Soon the sound of materialisation issues through the ship. Jamie hopes they've arrived in Scotland.

Unfortunately, the scanner shows nothing but a field of stars in a sea of blackness. The ship appears to be suspended in space. Outside, the police box shape hangs in the darkness of space, but something is happening to it. A thick, cobwebby substance begins to form around it.

The Doctor and his companions check all the TARDIS systems and determine that everything is still functioning normally. They have landed, but not really. Victoria gasps as she looks at the scanner and tries to draw the Doctor's attention. As they watch, the entire screen is obscured by the spreading of the web.

The Doctor concludes that someone or something is holding them here.

Back on Earth, a full-blown military emergency exists. A group of soldiers are holed up in an underground HQ. It appears that they have been down here for some time and have a full command centre organised. Corporal Lane is addressed by another Corporal, looking for their C.O., Captain Knight.

Knight is in another part of the HQ, being interviewed by an obsequious civilian called Harold Chorley, a journalist for London Television. Knight is speaking fondly of their former C.O., a Colonel Pemberton. Pemberton has apparently been recently killed in action and Knight speaks highly of his sacrifice. Chorley is very happy with the quotes, showing a lack of compassion a mile wide.

The Corporal arrives to report that Professor Travers has arrived, only to be pushed aside when the man himself bursts in. Travers has been brought here against his will and is none too happy about it. Knight tries to calm him down, telling him that his daughter asked for him, to help in the emergency. Knight is none too happy about it either, considering this a military matter. However, others above him disagree and wish to have the scientists working on the problem as well.

Travers notices Chorley and begins badgering him. Chorley identifies himself as the sole journalist assigned to cover the emergency from the front lines. The government chose one and only one person to report and he was the lucky one. He takes the opportunity to ask Travers some questions about his plan to fight the "menace". Travers is at first snappish and dismissive, but he then grabs the mousy reporter's microphone and speaks clearly into it. He says with a calm sense of finality that this menace most likely will not be defeated. London and perhaps the whole of England could be completely wiped out.

The chatty Chorley is at a loss for words at this dire pronouncement.

On board the TARDIS, the Doctor works on a small black box, attaching a component provided by Jamie. He says that whatever is holding them here will have to let go sometime. When it does, this box will help them to break free.

Out in space, the Doctor's prediction come true. The webbing begins to fade away from around the TARDIS.

This clearing shows on the scanner and Victoria is ecstatic. The Doctor plugs his machine into the console and urges his companions to hang on. The TARDIS continues on its way, preparing to land. Just before it does so, the Doctor activates the box and a high-pitched whine fills the room. Suddenly there is a jolt and they are all thrown to the floor.

The sound is gone and as they stand back up, it appears that all is well. The Doctor tells them that he used the box to move them on a bit from where they were supposed to land - perhaps half a mile. They have managed to elude their captor for the moment.

The scanner simply shows a curved tile ceiling in gloomy light. No way to tell where they are. They shall have to go outside to find out. Victoria asks if it's safe and the Doctor doesn't think so for a moment. Jamie goes to fetch some torches.

They've landed inside some sort of building but a sturdy metal grille blocks the way out. They find a flight of steps and descend. All the walls are tiled and all the ceilings are curved. The stairs lead to a sort of platform, beneath which is a dark trench of some sort. Victoria draws their attention to one of the white tiled walls. On it, coloured tiles spell out the words "Covent Garden". The Doctor puts it all together and deduces that they've landed in an Underground station in London. This is the platform. He tries to explain the underground trains to his companions but has little success. Victoria at least knows what a train is!

Victoria is concerned that it is so dark down here, but the Doctor thinks it's just the middle of the night. They should go back upstairs to find the way out. As they go, the Doctor comments on how funny it is they seem to keep landing on Earth recently.

Upstairs, they find the way outside, but it too is barred by a metal gate. They can see clearly that it is broad daylight outside. No reason for the station to be closed...nor for there to be complete silence all around them. It is very odd indeed.

Jamie spots a man sitting on the other side of the grille and goes to ask him what's going on. However, the man is quite dead and covered in cobwebs. His body topples over, revealing a news banner reading "Londoners flee! Menace spreads".

The three travellers trudge back downstairs to the platform, lost in thought. Victoria is horrified by the dead man's cobwebbed body and doesn't want to go on, but the Doctor insists. They must try to get above ground at the next station.

Jamie suddenly jumps from the platform into the trench, causing the Doctor to shout in alarm. He urges Jamie to stay still, although the lad cannot figure out what he's done wrong. The Doctor leans down and measures the metal rails with a small instrument. Mercifully, the meter reads zero, indicating that there is no electricity flowing through the rails. He tries to explain that Jamie could have been electrocuted if he'd touched active rails, but it seems to go past him. The Doctor and Victoria jump down in the rail bed with him and head off along the tracks.

Along the way, the Doctor tests the tracks. There is no electricity and no grease along them as well. In fact they are dusty. They haven't been used for quite some time, which is very puzzling. Jamie spots a power cable running independently along the rail bed. It doesn't appear to be part of the rail system.

Suddenly a row of electric lights strung along the top of the tunnel come on, bathing the tunnel in light. The Doctor, Jamie, and Victoria hide in a cubby hole. A group of soldiers move along the tunnel, carrying a spool of cable which they unwind as they go. Jamie wants to go and ask them what's going on but the Doctor urges caution. He sends Jamie and Victoria to follow the soldiers and keep an eye on them. He is going to follow the power cable to see where it leads. They are to meet back here in a few minutes.

The three soldiers, Corporal Blake, Staff Sergeant Arnold, and Craftsman Weams continue their work unrolling the cable. Weams suddenly stops when he hears something in the tunnel behind them. Arnold chides him for being jumpy and Blake urges them to get on with the work.

Jamie and Victoria stop as the soldiers do. They strain to hear movement but can hear nothing. Jamie thinks they must be moving again and they start forward. Unfortunately, Victoria's face brushes against a spider web and she cries out, stepping backward involuntarily.

All the soldiers hear it and Weams tells the others he told them so. They all turn and go back up the tunnel.

Jamie chides Victoria for her jumpiness and the girl apologises. They can only hope the soldiers didn't hear them. They continue on. The soldiers, however, are hiding in an alcove and step out as Jamie and Victoria pass. They are captured.

The Doctor has followed the power cable to the next station - Charing Cross. The cable is attached to a pile of crates on the platform. As he investigates, he hears a frighteningly familiar bleeping sound and jumps back into the rail bed beneath the platform. It is the sound of the robotic Yeti he fought in Tibet several adventures previously.

He cannot imagine what they are doing here in London. He presses himself into the darkness as the Yeti stands over the crates on the platform.

Captain Knight stands worriedly over Corporal Lane at the R/T. Lane is trying to raise one of their units which is 20 minutes overdue from Holborn. Lane says he's sure that things are all right, but he may just be trying to convince himself. Knight orders him to continue to try and raise the unit.

Anne Travers arrives with a blast recorder she has repaired. She is in charge of the scientific section of this mission, a situation which pleases Knight no end. He seems quite taken with the beautiful and capable young woman.

Chorley bursts in, protesting about his continued mistreatment by Professor Travers. He is being obstructive and secretive and Chorley will not stand for it. As diplomatic as he can, Knight tells him that now is not the time for talking. Travers is busy and will surely have time for a sit-down soon. He then bustles Chorley out of the room.

The Doctor hears a second bleeping on the platform and peeks out to see a second Yeti arriving. He ducks back down quickly. The two robots have small gun-like devices in their hands, which they aim at the crates. They are web guns which quickly cover the crates in the thick webbing that encased the TARDIS.

Staff Sgt. Arnold and his men return to HQ, bringing Jamie and Victoria with them. Arnold orders the cable taken up to the operations room while he goes to find the Captain.

Knight continues his relentless pursuit of Anne Travers, trying a lame pick up line, which she promptly shoots down. Things are not going well, yet he is still enjoying the pursuit.

Arnold bursts in, reporting that the operation was a success. Weams and another soldier bear the cable upstairs while Arnold tells Knight of the "present" he has brought back. Knight wants to question them, but he doesn't have the time. He's got a demolition job to complete. However, Anne intervenes with a question. Were there any more civilians down in the tunnel? She doesn't like the idea of going ahead with blowing it up if there might be more innocent people hiding there. Knight and Arnold hadn't thought of this. Arnold heads off to question the prisoners.

Arnold takes over from Blake, who had been guarding them, and herds them into the common room. Jamie asks the first questions. However, Arnold doesn't believe Jamie doesn't know what's happening - why the military is down here and why the Underground has been locked down. He wants to know if they were alone down there. Jamie decides to keep quiet about the Doctor and stops Victoria from revealing his presence as well.

The Yeti complete their task of smothering the crates and lumber off. The Doctor scrambles up onto the platform to investigate.

Jamie continues to insist that he and Victoria were alone in the tunnel, despite Arnold's continued questioning. At last he is satisfied and reports to Captain Knight. They are clear to fire.

Jamie wonders what they're talking about and is shocked when Arnold reveals the truth. They are going to blow up the Underground tunnel! The cable connects to a mass of explosives. Victoria is horrified. What about the Doctor?

Knight returns to Weams in the operations room and orders him to activate. No time to waste. Weams presses the plunger.

In the Army's HQ, Jamie and Victoria bang on the common room door to be let out. They are trying to attract anyone's attention. No one responds and they both despair that they are too late to save the Doctor. Both of them blame themselves for leaving the Doctor in the path of the explosion.

Some time later, Sgt. Arnold has reported the Doctor's presence in the tunnel to Captain Knight. They believe that he must have been caught in the blast and there is little they can do now, but Arnold would still like to go down and search for him. Knight agrees and heads off.

Craftsman Weams reports to Knight that the blast recorder that Anne recently repaired is apparently not working. It did not register during the explosion. Knight thinks this rubbish but Anne sees that it's true. Nothing registered. Come to think of it, the sound of the blast was not audible here at HQ either. The circuits showed that the blast was fired, but there was no explosion of note. Very odd.

Weams suggests that this mysterious Doctor might have had something to do with it. Perhaps he found and tampered with the explosives. The charge of sabotage concerns Knight. He will go and speak with the two young people.

Victoria tries to reassure Jamie that he was doing the right thing in keeping the Doctor's presence a secret. They still don't know if they can trust these soldiers.

Knight and Anne enter the common room, followed by the pesky Harold Chorley. Anne takes a moment to try and reassure the worried Victoria. They think that the Doctor might not have been hurt in the blast and some men have been sent to find out. Knight questions them about what they were doing in the tunnel in the first place but is interrupted by Chorley. His question is inane and derails the discussion.

Suddenly the whole interrogation is ended when Weams bursts in. Corporal Lane has finally raised Holborn on the R/T. It sounds like they've run into trouble with the Yeti. Knight leads the way out, followed by Weams and Chorley. Clearly there's bigger fish to fry.

Anne is left with Victoria and Jamie. Jamie is stunned by what he just heard. Yeti!

Lane tries desperately to get someone to respond on the other end of the radio. Knight arrives and asks for an explanation. They have a link, he is told, but no voice. It's just firing. Listening in, Knight hears the distant sounds of roaring gunfire. Chorley is appalled.

Lane explains that he did speak with one of the men a while earlier. Sounded like something went wrong from the start. They were there to unload ammunition but the truck was late. The ammo got unloaded, but then they were ambushed by Yeti. Knight moves into action, determined to get there and find out what's happening. Lend a hand if possible.

Chorley can't believe the soldiers are deliberately going into that fierce battle he heard. Knight says he is and invites the mousy little man to come along. Chorley declines, as Knight had expected.

Arnold and Blake reach Charing Cross Station and are not surprised to find it still standing. The explosives still sit on the platform, but the crates are decimated. They all lie under the thick cocoon of webbing. All indications are that the explosives fired. Why then wasn't the tunnel destroyed? It is a clear case of sabotage and the Arnold suspects the mysterious Doctor.

Professor Travers works in the HQ laboratory. He has on the bench several artefacts from his journey to Tibet - including another Yeti control sphere. As he examines it, Anne enters. She tells him about the two young people brought in by Arnold and Blake, and she tells him that they seem to know a great deal about the Yeti. They even know about the control spheres, which was not public knowledge. Travers is concerned and goes off to speak with them.

Jamie and Victoria are putting together all the clues they've gotten. If the Yeti are here in the Underground, then the Great Intelligence is here too, controlling them. Jamie is certain now that it was the Intelligence that trapped them in space and brought them here to this time and place. But why?

Travers bursts into the common room and begins firing questions at the two young people, his tone accusatory. Jamie fires back and chaos abounds. However, Victoria has stayed quiet, examining the face of the old man before them. She silences Jamie as she realises who the man is. She identifies herself and Jamie to him and the same realisation dawns on him. Travers is stunned to see Jamie and Victoria again, looking just as they did over 30 years ago. Time has marched on for him since their meeting in Tibet. He is old and they are still young.

Jamie at last recognises him too and is very glad to see him again. Travers is stunned to realise that the Doctor was telling him the truth about his "time machine" all those years ago. That is the only explanation of it. He can hardly believe what he is seeing. Travers is concerned to hear that the Doctor is lost in the tunnels. He is desperate to find the Doctor, ignoring Anne's questions. He grabs Jamie, prepared to go outside and look for the Doctor. He tries to explain to his daughter about the time machine but cannot do so adequately. He leaves Victoria to do it for him and heads off with Jamie.

Anne looks to Victoria for an explanation. This will be very difficult indeed.

Arnold and Blake return to find that Knight has gone to Holborn. Chorley is in ops as well, despairing that all of the men on the ammo run are dead. Arnold chastises him for his pessimism and takes over in ops.

Jamie and Travers arrive to see if Arnold found any sign of the Doctor. They're sure he wasn't killed in the explosion because there was no explosion, and Arnold is sure it's because of him. Travers dismisses this gruffly. The Doctor is a friend and he is also the one man who can help them against the Yeti. Arnold finds this hard to believe but he is willing to go out again and search if Jamie goes with him. The lad says he thinks he might know where the Doctor is. This is a bit of a lie, but it convinces Arnold. The two men head outside immediately.

Anne is finding Victoria's explanation of the TARDIS very hard to believe, even though her father obviously does. But it's clear that she and Jamie know about what went on in Tibet and that was over 30 years ago. Neither of them are old enough to have lived that long so it must be true. She wonders then why her father never mentioned the Doctor or the TARDIS before. Probably because it is so hard to believe.

Chorley enters, saying he's come for his typewriter. However, he takes the opportunity to pump Anne for information on the Doctor and these two young people. Anne is evasive and gives flip answers, angering Chorley. Acidly, Anne explains that Chorley has a reputation for distorting the truth. He is a sensationalist and everyone knows it. Chorley bristles at this characterisation, but he cannot deny it. He stops short of branding Anne with a snide epithet and reminds her that he has many who follow his words. He promises to reveal all that goes on down here when this business is over and he's free to report. Anne reminds the cowardly man that he may not get out at all.

Chorley turns on Victoria, saying that she and her friends might be the cause if indeed they don't all get out alive. He finds it quite a coincidence that the Doctor and his friends turned up when they did. He reveals that there was no explosion in the tunnel and the belief that it was the Doctor who sabotaged the explosives. Victoria says that if he did, it was for a good reason.

Chorley takes great pleasure in telling the nervous Victoria that Jamie has gone out into the dangerous tunnels with Arnold to try and find the missing Doctor.

Captain Knight and Corporal Lane have been successful in reaching the unit at Holborn. They and their men have managed to retrieve some of the ammunition that was being unloaded there and brought it back down into the tunnel. Knight sends Lane to bring the rest of their men back from above where they are working hard to hold back the Yeti.

However, Lane does not get far before he is confronted by Yeti and is forced to open fire himself. Unseen by Knight and the others, the battle rages. The sound of Yeti web guns fills the tunnel, followed by a scream. Lane falls back and joins Knight. It was no use. Their bullets had no effect. Two Yeti are approaching. Suddenly, some of the men spot two figures approaching from behind them. It is Staff Arnold and Jamie. Knight and his men fall back to join them.

Knight tells Arnold in one word what is happening: Yeti. He has devised a plan, though. The ammunition cases still sit on the rail bed, between them and the Yeti. He plans to try and detonate the lot by firing at them, hoping to catch the creatures in the resulting explosion.

Knight gets into position to open fire as the Yeti appear in the tunnel. Unfortunately, they make straight for the ammunition cases and cover them with thick webbing. Knight fires and the cases explode, but just like at Charing Cross, the explosion is smothered by the webbing. The boxes under the webbing pulse with light and a muffled sound reverberates through the tunnel. The explosion has been stopped.

Knight is stunned. He orders his men to retreat, but they turn to face two more Yeti coming at them from behind.

Professor Travers is angry at Chorley for deliberately frightening Victoria. He had no right to do such a thing. Anne sympathises, saying she sent the girl off to make tea to keep her mind occupied. The two of them now work in the laboratory on one of the control spheres.

Anne chats idly, speculating that the Doctor might not be what he seems. She disbelieves the story about the TARDIS and thinks it oddly coincidental that the Doctor has turned up on both occasions that the Yeti have. She thinks that he controls them.

Travers starts to respond but they are interrupted by Victoria, bearing a tray of tea. She seems distracted and decides not to have any herself. She says she's going to lie down, but she has actually overheard their conversation and is now very worried. She goes off.

Anne is concerned and wonders if she might have overheard but Travers dismisses this. He also strongly dismisses Anne's cavalier thought about the Doctor. He has seen with his own eyes the Doctor defeat the robots and save Det-sen monastery. He is no more in league with the creatures than she is. Anne apologises for jumping to conclusions and sets back to work.

Knight and his men stand nervously between the two sets of Yeti. They are not moving and the men are getting nervous. Jamie reveals some knowledge of the robots which concerns Knight, but Arnold smoothes this over. He says that Travers has vouched for Jamie and his friends. Their knowledge of the Yeti is valuable.

However, before Jamie can offer his expert opinion, the Yeti come back to life and lumber off, completely ignoring the humans captive between them. Knight and the others are stunned, but pleased. They can now return to HQ. Jamie wishes to follow them, to try and see what they're up to, but Knight drags him along, not wanting to push their luck.

In ops, Corporal Blake and Craftsman Weams speculate on the source of this menace. Weams doesn't believe for a minute that these creatures come from Tibet. His money is on outer space. Surely that's clear enough. Blake doesn't think much of the Tibet theory either, preferring to picture a foreign power as their enemy - using a robot army and bacteriological warfare against them. They must be robots because bullets don't harm them...unless you get them right between the eyes. Hand grenades seem to work to, but they're all out of those. Now that the Holborn run's been stopped, they've got precious little ammo at all. A sobering thought.

Blake goes to get more tea and Weams' gaze travels up to a lighted map of the London Underground. The lines are picked out in bright white light, but several sections are blacked out - those affected by a weird sort of fungus which is engulfing the Circle Line. More of the line winks out as a frightened Weams watches. The fungus is on the move again, engulfing Euston Square and heading toward Kings Cross station.

In the laboratory, Anne helps her ageing father with a delicate adjustment to a circuit. He wishes that the Doctor would turn up. That's the help they really need to fight this menace. Blake appears and tells them about the fungus. Travers and Anne follow him up to ops.

By the time they arrive, Kings Cross is already blinked out and the dark line continues to move on toward Faringdon. It has never moved this fast before; in fact it hasn't moved at all in three weeks. Chorley, who has also gotten in on the confab, believes the Doctor is to blame for all of this, including the fungus. He speculates that Jamie and Victoria are spies. Travers denounces this, saying that Jamie wouldn't have gone away and left Victoria if he was a spy. However, Blake notes that Victoria has not been seen in some time and no one knows where she is.

Spurred on by Anne's suspicions about the Doctor, Victoria has gone herself into the tunnels to try and find him. It is all she can think to do. If she could only find him, he will sort all of this out. Unfortunately, she has had no luck in finding anyone at all.

A search of HQ turns up nothing and Chorley is convinced that this proves him right. Just a couple of spies. On the map, the fungus continues its move, engulfing Faringdon and moving on toward Liverpool Street. Blake can only hope that Knight and Arnold aren't in its path.

Blake and his men head back to HQ but are stopped by the sound of singing echoing through the tunnel. A lilting voice signs scales. All of the men hide as the voice grows closer. They are surprised to find it is a soldier. A little man in the uniform of a private. He is very glad to see the other soldiers. He seems a bit shell-shocked and says he'd been singing to calm his nerves. He is a Welshman called Evans. He reveals that he was the driver on the ammo truck to Holborn. He managed to escape into the tunnels during the fighting and has been trying to find his way out ever since. He's also been trying to avoid some "cobweb muck" moving down the tunnel.

Knight is concerned to hear that the fungus is moving again. Evans also says that he saw a Yeti "leading" the fungus mass; a Yeti carrying a glass pyramid. Jamie remembers the pyramids used by the Intelligence in Tibet. If they can find it and smash it, they can put the Intelligence out of action.

Unfortunately, this is the first that Knight or any of the others have heard about any "Intelligence" and they don't credit the story. When Knight learns that Kings Cross was engulfed by the fungus, he fears for HQ and decides to head out.

Jamie resists, still hoping to find the Doctor down here. He also would like to have a go at that glass pyramid. He will not comply with Knight's order and so he is allowed to stay behind. Surprisingly, Evans volunteers to go with him. Knight agrees and he and his men head back to HQ.

Jamie thanks Evans for his help and is shocked by the response. Evans is only looking for the way out. The first chance he gets, he's leaving the tunnels.

Tension is growing in the HQ as the fungus spreads through Liverpool Street. It seems clear that the fungus is planning to meet up with itself through the Circle Line and cut off the city of London. If that happens, HQ is finished. Weams suggests evacuation while they still can, a sentiment Chorley approves of. Travers resists, saying that only Captain Knight can order an evacuation. But there is no sign of him. They can only hope he's not trapped on the Circle Line.

Evans has led Jamie in circles along the tunnels. They are at Cannon Street station on the Circle Line before Jamie realises there are maps at each station. He chastises Evans but is quick to be off again. Evans follows, still only interested in finding an escape route.

Knight reaches HQ and learns of the movements of the fungus. Chorley brings up the idea of evacuation and Knight rounds angrily on him. If Chorley wishes to run, he is welcomed to do so. Knight reports no sign of the Doctor in the tunnels. He is concerned to find out that Victoria is gone two. Now all three of these strangers are out there in the tunnels.

Victoria continues to wander the tunnels, calling out for the Doctor and Jamie. Unbeknownst to her, she is being followed by a soldier. One we have never seen before...

The fungus continues its relentless move around the Circle Line. The HQ is now cut off, but Knight is staying put. Travers continues to insist that the Doctor is their only hope, but Knight believes he must be dead by now. The only station left on the Circle Line is Monument.

Coincidentally, Jamie and Evans have arrived at Monument, heading for Tower Hill. However, a strange noise reaches their ears. A pulsing sound begins to grow in intensity, moving toward them. A faint light grows brighter along with it, emanating from the tunnel.

Jamie senses it first - the fungus is here. They are trapped in both directions. Evans becomes more and more frightened as they look for somewhere - anywhere - to run.

Looking around desperately, Jamie spies a potential exit via an archway. They start to go toward it but are stopped in their tracks by the sight of what is coming down the tunnel at them. Not only the glowing fungus, but also a Yeti. It seems to be leading the fungus somehow... and it carries a glowing glass pyramid.

Remembering his previous encounter with the Yeti, the glass pyramid is the control centre for the Intelligence. Destroy that and you destroy the Intelligence's link with Earth. Jamie urges Evans to use his rifle and destroy the pyramid. Evans, not the best of soldiers and extremely shaky even without the incentive of fear, has trouble hitting the mark. Finally, on the fourth shot, he manages to hit the pyramid. It explodes in a shower of glass.

To his horror, Jamie sees that it has done nothing to slow the advance of either the Yeti or the fungus. He is dumbfounded, almost too stunned to move. Evans shouts at him to go before it's too late. They both run for the archway, escaping just as the fungus fully engulfs Monument station.

Victoria still wanders in the tunnels, calling out for the Doctor. It is very dark and she is very frightened. Suddenly she is stopped by a figure from behind. It is the soldier who has been following her for some time. He is a Colonel by rank and wears a tartan headband around his hat. Just as he stops her, the Doctor steps out from the darkness. She is very glad to see him, but the Colonel cuts short their reunion. He wants to know if there are any more civilians down here.

The Doctor, realising that the Colonel means business, tells him about Jamie but wonders where he is. Victoria explains that he left the HQ at Goodge Street to come looking for the Doctor. The Colonel hears this and wonders if these civilians aren't something to do with Travers and his daughters, the only other civilians he knows of down here.

The Doctor reacts to the name and Victoria tells him that Professor Travers is here - the same man they met in Tibet. However, she also says - mistakenly - that Travers believes the Doctor is responsible for the Yeti. The Colonel has heard enough. He pulls his gun and urges the two of them back to HQ.

In the operations room, Captain Knight is none too pleased to see that the fungus now has them completely surrounded on the Circle Line. Corporal Lane reports the arrival of Victoria and the Doctor, along with the mysterious Colonel. Knight decides to go and talk to them all, and he instructs Anne to go and fetch her father to talk with the Doctor. Staff Arnold is left in charge in ops, wondering aloud with Weams about all the comings and goings here at HQ.

The Doctor and Victoria, under guard in the common room, whisper to one another, getting up to speed on events. The Doctor explains that he was knocked out by the explosion at Charing Cross but otherwise unharmed. When he came to he wandered the tunnels until he met up with Victoria and the mysterious Colonel. No one seems to know about him. The Doctor had deduced that the Intelligence was here on Earth once he saw the Yeti. And now he knows that Travers is here, it all starts to add up.

Knight arrives and first addresses the Colonel, who identifies himself as Lethbridge-Stewart. He is here to take over operations from the late Colonel Pemberton. Knight is a bit surprised by this and asks for his authorisation. The Colonel is glad to see that Knight is cautious and produces the papers. He explains that he was part of the ammunition party at Holborn. He was the only one who managed to survive the battle with the Yeti. Knight tells him about Evans, who also thinks he was the only survivor, and wonders why they didn't know about each other. Lethbridge-Stewart says the scene was very confused in the battle.

He said he made his way toward HQ as soon as he could, then ran across the Doctor and Victoria. Knight tells Lethbridge-Stewart that Professor Travers has already vouched for the Doctor and in fact they know more about the Doctor than they do about the Colonel himself. There is clearly a bit of distrust on Knight's part.

Travers bursts into the room, delighted to see the Doctor again. They shake hands joyously until Colonel Lethbridge-Stewart interrupts. The grumpy old scientist has little time for talk of new CO's and is ready to get the Doctor's help immediately. The Doctor vouches for Victoria and the three of them are off to the lab without another word to Lethbridge-Stewart. The Colonel seems put out that Travers seems to be in charge down here. Captain Knight tells him dryly that it is probably best that way.

In the laboratory, the Doctor examines a Yeti control sphere, opened and nearly gutted by Travers as he explains again what happened to him in the tunnels. Anne and Victoria stand by as well. The cobweb/fungus proves to Travers that it is the Intelligence they are dealing with. The Doctor agrees, glad to see that Travers doesn't really think he is responsible for it, as Victoria said. Anne had feared that Victoria was listening in to them and Travers denounces the idea to the Doctor just as vehemently as he denied it to Anne before. If only Victoria had been listening then.

The Intelligence is here and it brought the Doctor here for some reason. If only they knew why. The Doctor has a larger worry on his mind for the moment - Jamie.

In the tunnels, Jamie and Evans have re-emerged into the tunnels on the Central Line, at Saint Paul's station. Jamie is ready to strike out again, but Evans holds him up. There's a vending machine nearby and he's hungry for some chocolate. Jamie is shocked at this frivolity, with Yeti right on their trail. As Jamie heads off, Evans continues to complain about how he shouldn't be down here at all. He's just a driver. Just for a lark, he tries the machine without having put any coins into it. To his surprise, he gets a bar of chocolate. Must be his lucky day.

Back at HQ, Chorley's nerves are starting to fray. He's getting desperate for a way out. Staff Arnold tries - with all the diplomacy he can muster - that there is no way out. The HQ is at Goodge Street, completely surrounded by the fungus on the Circle Line. Chorley suggests one of the other lines intersecting here - going out underneath the fungus. But Arnold explains that the fungus extends both upwards and downwards from the Underground. They're well and truly trapped.

Chorley insists there must be a way, saying that he must get his reports out. Clearly that is not his intention, but when he suggests a passage to the surface, Arnold must tell him the truth. There is a ground level door in Cheney Street. That's all Chorley needs to hear. He's off in a flash, looking for the escape route, leaving Arnold and Weams to complain about the crazy civilian.

In the laboratory, Travers explains sadly that he is the cause of all this trouble. He brought the Intelligence back to Earth. He explains that he brought a lot of stuff back here with him from Tibet - broken Yeti, control spheres, etc. He had been fiddling with one of the intact spheres on and off for years, trying to understand how it worked, and then one day it activated and came to life. It disappeared on instructions from somewhere, making for the nearest Yeti. Then the Intelligence returned.

Captain Knight interrupts the group, announcing that Colonel Lethbridge-Stewart has called a briefing. Travers and the Doctor head off, leaving Anne behind for the moment. Before she goes, she asks Knight if there's been any news of Jamie. Unfortunately, he has heard nothing.

Jamie and Evans continue their trek through the tunnels, this time with Evans in the lead. He is excited as they are nearly at Chancery Lane, the station where he's getting out. He figures that he can get back to Holborn easily from there and back to his lorry. Jamie is disgusted at this seeming cowardice, but Evans won't be shamed. He's not supposed to be down here - a driver, he is. The soldiers at HQ don't stand a chance against the Yeti and he's not staying around where he's not supposed to be, inviting death. He invites Jamie to do the same, which evokes a response of disgust. Evans is sure that his course will prove the smarter.

The briefing begins in the common room, complete with slides. This is quite an education for the Doctor as he learns of the progression of the invasion. First there was a fog or mist on the surface, all around London. The mist is not poisonous, but anyone who goes into it just doesn't come out again. The whole area was cordoned off, but the mist continued to expand. Two days later, fungus was reported in the Underground and the tube system was abandoned. Two days after that, the first Yeti were sighted.

The Doctor looks at the slide of the Yeti and has his suspicions confirmed. He didn't get a good look at the creatures in the tunnel but now he can see for certain that they have changed in appearance. A sort of Mark II. The briefing continues, showing that as the fungus spread below ground, the mist spread above. Now that the fungus has completely filled the Circle Line, it is safe to assume that the mist has covered the ground area above as well. No chemicals or explosives have worked against either substance.

The Colonel tells the Doctor, Travers, and Anne that their hopes are pinned on them. If they fail, London's finished. Anne explains that she and her father are working on a plan to try and jam the transmissions from the Intelligence to the Yeti, but they need additional equipment. Knight says that they have very limited communications outside the HQ. The mist absorbs all radio waves and telephone lines have been cut by the Yeti. There are still some lines between here and Holborn, but they may not last long.

Chorley bursts into the room and disrupts the meeting to report the surface door that is available to them. He tells the Colonel that a helicopter could come and pick them all up and take them to safety. Perturbed, Lethbridge-Stewart tells him there's no way to call a helicopter and orders him to sit down. He starts to protest, being a civilian and all, but that is a double-edged sword. Being a civilian, he ranks lower than last in importance. Angered, Chorley storms out.

The Colonel is ready to do some constructive thinking about their dilemma.

Chorley runs into Weams in the corridor, asking about tall buildings in their vicinity. Weams knows the Post Office Tower isn't far and Chorley thinks it might be tall enough to be above the mist, therefore a prime spot for sending radio signals. However, when Weams goes to show him its location on the map, he sees that the fungus is on the move in the tunnels once again. He hurries off to report it.

Jamie is now alone in the tunnels, travelling toward HQ. However, hearing a noise behind him, he hides, jumping out when the shadowy figure passes by. To his surprise it's Evans. The little soldier goes on and on about not abandoning his mates and doing the right thing, but Jamie guesses the truth - he couldn't get out.

Grudgingly, Jamie allows Evans to rejoin him on his trip to HQ.

Lethbridge-Stewart is stunned - four tube stations all swallowed up by the fungus in half an hour. It is at Chancery Lane now, and still moving. At this rate, the HQ will be inundated in a couple of hours at most.

Chorley starts in on the Colonel again, begging for him to do something. However, Lethbridge-Stewart turns the tables on him and suggests that he himself do something. Chorley is to set up shop in the common room to act as a sort of liaison officer, a central point of information for all of them in the activity to come. All of them will report their progress to him directly. Lethbridge-Stewart says all of this very quickly and very matter-of-factly, before Chorley can protest. Blake is to see to it that he has everything he needs and he rushes the two men out.

Once they are gone, Lethbridge-Stewart admits that he just made up that assignment to keep Chorley occupied and out of their hair. Now they can think.

The Doctor suggests blowing up the tunnel just outside the Goodge Street station, thus sealing them safely away from the fungus for a while. The Colonel likes this idea, and Arnold says he thinks they've just enough explosives left to accomplish the task. However, they must be able to detonate them without the Yeti smothering them like they did at Charing Cross. The Doctor suggests using something moveable, something that can move along the track. Knight suggests a baggage trolley, sending Arnold off to find one that he knows is around here somewhere.

They will put the explosives on the trolley and set a triggering device. They'll send the trolley down the line and detonate it when it is in position. The Colonel likes this idea and the Doctor and Travers go off to build the detonator. Satisfied that they are doing some practical work, the Colonel decides to take a quick tour of the HQ while waiting for the trolley and explosives to be organised.

At the entrance to the HQ, unseen by anyone, the massive doors are unbarred and left open. There is a traitor at work among the staff of the HQ.

The Doctor returns to the lab to find Victoria and Anne. Travers is not with them. Victoria is examining one of the small model Yeti on the bench. They were used in Tibet to guide the robot Yeti. She shudders at the memory. Luckily, it doesn't work. None of them do. However, Anne notices that one of them is missing. Where can it be.

The same person who opened the fortress' doors is now at the door to the explosives store. A hand places the missing Yeti model in front of those doors where it begins to emit a bleeping noise, calling out to the real Yeti.

In the tunnel, a motionless Yeti comes to life and begins moving toward the HQ.

Travers arrives in the lab with a complete detonator, including timer. The Doctor is pleased. Meanwhile, Victoria and Anne have been speaking quietly together. Anne pipes up with their grim conclusion. The explosion may seal off the HQ from the fungus, but it will also prevent Jamie from reaching the place as well. He'll be trapped in the tunnel!

The Yeti, now moving silently, enters the HQ through the open main doors. No one is around and it walks straight in, its goal nearly in sight.

The Doctor presents the detonator to Colonel Lethbridge-Stewart. It has a 60 second timing device on it but will also go off if the Yeti try to tamper with it. All they must do is push the explosives trolley down the tunnel and get clear. Staff Arnold reports that the trolley is now on the lines and ready to go. However, he reports that the main door was standing open when he went past. The Colonel is stunned. Shortly, Blake arrives bearing the badly damaged padlock to the explosives store. He also found the missing model Yeti outside the store room.

Everyone is very worried, especially the Doctor. Blake didn't look inside the store room and simply left Corporal Lane on guard. Lethbridge-Stewart, Arnold, and the Doctor head for the store room. Weams seems overly curious about the Yeti model and takes it from Blake to examine it more closely.

There is no sign of damage at the explosives store other than the missing lock. It seems very quiet. While Arnold goes to shut the main door, the Doctor decides that they must take a look inside the explosives store. It is very quiet and he is optimistic. However, as soon as he cracks open the door, he knows he was wrong. The store room is full of the pulsating, glowing fungus! It immediately begins expanding outward.

The Doctor tries desperately to close the door and force the fungus back, but it is too strong. All of the soldiers pile on and together they manage to close the door. But that is the least of their problems. They now have no explosives with which to blow up the tunnel.

In the laboratory, Victoria still laments over what the explosion may mean for Jamie. Anne and Travers try to reassure her. Perhaps he's already out of the Circle Line - perhaps he got out before the fungus sealed it up. Travers agrees, telling her that the Doctor will soon sort out this mess and she'll be reunited with Jamie. The Intelligence doesn't stand a chance against them now.

Colonel Lethbridge-Stewart has decided to continue with the plan to blow up the tunnel. A party of men will try to get through the tunnels to Holborn and pick up the explosives left there when the Yeti attacked. The Doctor thinks this a foolhardy plan, as he is certain the Yeti must have attacked the other explosives as well. However, it is all they've got and the Colonel decides to go on with the plan. Captain Knight will lead the first party, and the Colonel will go with Staff Arnold to bring up the rear. Arnold is sent to inform Travers... but not Chorley!

Lethbridge-Stewart assures the Doctor that he will be quite safe. Four men will be left at HQ to guard it. However, the Doctor is not so sure. He brings to the Colonel's attention the fact that someone here at HQ is in league with the Yeti. Someone opened the main door so the Yeti could come in. It could be anyone, the Colonel included.

In the common room, Victoria is foolishly explaining to Chorley how she and her friends came to be in the Underground. Chorley doesn't pretend to understand what a TARDIS is, but he does realise that if it got here, it can get out...and take all of them with it. Victoria assures him the Doctor won't run. To make matters worse, she tells Chorley about the imminent destruction of the tunnel and how they will all be trapped in the HQ. He is shocked. No one had told him, and clearly that was for good reason. Chorley leaps from the table and races out, nearly knocking the Doctor over in the process.

The Doctor has come to find Victoria and is disturbed by Chorley's behaviour. Victoria explains what she told him and the Doctor becomes very worried. Victoria now realises what she's done and is abject in her despair. She may have cost them all their escape. The Doctor heads for the door, only to discover that Chorley has closed and locked it. They are trapped.

Chorley races for the main entrance, only to run into Jamie and Evans as they arrive. They tell him that they passed the soldiers on their way to Holborn but Chorley seems little concerned. He's still got time and he races off into the tunnels.

Jamie and Evans are puzzled by this behaviour but do not think enough of it to follow him. Instead, they go inside. Jamie hears banging from an inside door and goes to find the source.

It is the Doctor and Victoria, banging to be released from the common room. Jamie lets them out and he is happy to be reunited with his friends. Jamie wonders why they were locked in, but the Doctor is more concerned about Chorley. He learns that he's just gone out and the Doctor leads the others after him.

Travers and his daughter continue work with the Yeti control sphere, puzzling over the extended absence of the Doctor, when a terrifying scream fills the air. Travers goes off to investigate.

He traces the scream to ops where he is horrified to see Craftsman Weams dead on the floor. Hearing a bleeping noise, he examines the body. Beside it is one of the model Yeti. He knows immediately what it means and he turns.

Travers is knocked unconscious by the Yeti. He slumps on the floor. Anne appears in the doorway and lets out a scream, afraid that her father is dead. The shock overwhelms her and she faints dead away. The Yeti turns its attention back to Travers, grabbing him and dragging him out of the room.

The Doctor, Jamie, Victoria, and Evans hurry down the tunnels in search of the errant Chorley. The Doctor is certain he's making for the TARDIS at Covent Garden and makes certain they are heading along the same path. Evans suggests exploring a different path, just in case Chorley took a wrong turning, but that doesn't matter. All that matters is that they beat him to the TARDIS.

Colonel Lethbridge-Stewart and Staff Sergeant Arnold traverse a different set of tunnels, trying to catch up to Captain Knight's group on their way to Holborn. They make contact, but the news is bad. Knight's group has encountered fungus in the tunnel just 100 yards before Holborn. It is as if the Intelligence knew what they were up to and made a deliberate move to stop them.

But Knight is not ready to give up yet. He suggests trying another line, reaching Holborn via Piccadilly. The Colonel likes the idea and so they set off, on a path that will take them past Covent Garden...

The Doctor and his friends are nearly to Covent Garden themselves when they run into a mass of glowing fungus blocking the tunnel. They cannot reach the TARDIS. The Doctor wonders whether Chorley was stopped by it as well, or if he managed to reach Covent Garden before the fungus arrived. If he was stopped, then where is he?

The Doctor takes a few steps toward the mass of fungus, alarming Jamie and Victoria. Jamie tries to stop him but the Doctor is determined. He wants to get a sample of the fungus for analysis. Evans provides a tobacco tin, at great personal sacrifice, for the Doctor to store the stuff in. The Doctor picks off a piece of the webby stuff, causing the entire mass to pulsate and move. He manages to get a few more samples before it starts encroaching on them, then the whole group runs for their lives.

Staff Arnold and Corporal Blake have done a quick recce of the tunnel ahead. When Blake goes off to bring the others, Arnold is left on his own. To his surprise, something is moving in the tunnel ahead. Luckily it is only Evans. The Doctor, Jamie, and Victoria join him. Knight arrives and the two groups recount their experiences. Fungus everywhere along their route. There is no way to reach Holborn or Covent Garden. As far as the Doctor's concerned, it's just as well. He wants to get back to HQ to show Travers the fungus sample and begin analysing it.

Arriving at HQ, the Doctor is shocked to see the main door wide open once again. Something is wrong. Inside, the place has been wrecked. Clearly the work of a Yeti. Jamie worries that there may still be some of the creatures inside, but the Doctor thinks not. Victoria is horrified as they pick their way through the debris.

They reach the operations room and find Anne unconscious. Evans helps her into a chair whilst the Doctor tends to her. She regains consciousness but is still very frightened of what she's seen. The Doctor reassures her as best he can that she's safe. She looks around and sees that her father is not here and she knows what has happened. He has been taken. She becomes hysterical and they'll get no more answers from her. Jamie and Victoria help the terrified woman down to the common room.

Evans wonders if Travers has really been taken. The Doctor thinks it very likely, although he can't figure why. Somehow the Yeti must have had some use for him alive.

Lethbridge-Stewart and Knight arrive, having heard about Travers. The Doctor reports that the Yeti broke in while they were out looking for Chorley. Knight thinks that Chorley ran out due to panic but the Doctor doesn't seem quite so sure about that. Arnold reports Weams' death and details Evans to help with the body. Before he goes, Evans tells the Colonel he's glad he survived the attack at Holborn. Once again, Lethbridge-Stewart seems unfamiliar with Evans. Odd.

The Colonel is puzzled about why the Yeti broke in and then left, but the Doctor knows the answer. They came for something and left as soon as they got it. They came for Travers.

Blake arrives and fetches them both to look at the map of the Underground. The fungus is on the move again. The map shows more of the lighted tunnels going dark, succumbing to the web fungus. It is closing in on Goodge Street. The Colonel sends Blake away to have a quiet talk with the Doctor and Captain Knight. He suggests that perhaps Travers was the agent working with the Yeti, but the Doctor doubts it. To him, Chorley is a more likely suspect. However, the agent could very well still be here. The Colonel hadn't discounted that possibility either.

With Travers gone and Anne traumatised, the Doctor is now the main scientific adviser to the military. He explains to Lethbridge-Stewart that the Intelligence is a formless mass floating about in space, but with a mind and a will. He doesn't know what it's after here, but he does know that it brought him here for some purpose. The Doctor is forced to explain about the TARDIS and how he came to be here. Knight can hardly credit the story of a time-space craft, but Lethbridge-Stewart is perfectly willing to accept it. Almost too willing. He too sees the TARDIS as a means of escape...if only they can get it here from Covent Garden. However, the Doctor refuses to leave even if he could. He must finish Travers' work and try to stop the Yeti and the Intelligence.

Jamie interrupts and asks the Doctor to come with him. Anne is feeling better and would like to talk to him. The Doctor goes, glad to be away from the two military men.

Once he is gone, Knight confides in Lethbridge-Stewart that he thinks the whole story crazy. Lethbridge-Stewart does not. Despite Knight's doubts, they are going to mount a mission to retrieve the police box from Covent Garden. The Colonel has his hopes pinned on the Doctor to solve this problem, but if he doesn't, they'll need some sort of escape route. This is the best he's heard so far. Knight has no choice but to go along with this, but he cannot really believe they're going to do it. He even suggests that the mysterious Doctor might be leading them into a trap.

Anne is feeling better, but she is still very worried about her father. The Doctor refuses to mount a rescue mission, certain they could never find him in the tunnels. Their only chance is to try and find the Yeti's central control source. The Doctor learns that Travers was nearly ready to test a control sphere with a control unit of their own and is certain that this is why he was taken. The Yeti knew he was on to something and had to stop him succeeding. And now it is up to him and Anne to complete that work. They hurry off to the laboratory.

Jamie and Victoria cool their heels, worrying about how it is that the Yeti seem to know their every move. It is very worrying. Victoria begins to wonder if the Doctor can defeat the Intelligence this time.

The Doctor surveys Anne and Travers' work and is very pleased. The sphere is still in pieces, but the control box is nearly complete. The plan is to try and override the Intelligence's commands using the control box, but both the Doctor and Anne know that it cannot do that as it stands. There is more work to be done.

They are interrupted by the arrival of Evans, bearing one of the model Yeti. He found it by Weams' body and though the Doctor should have it. The Doctor becomes very agitated, knowing that these models are used as homing devices by the Yeti. The suggestion is clear and Evans is appalled that anyone thinks he might be in league with the creatures. Anne sees with horror that the others are gone as well. Evans now becomes angry at the further insinuation and tries to take back his tobacco tin.

Retrieving the tin from Evans, the Doctor calms somewhat. He reminds the soldier that they are all under suspicion here, including he himself. This does little for Evans, who huffs off, reminding the Doctor that he expects his tin back when he's done.

Anne asks about the tin and the Doctor explains about his fungus sample. However, he is more worried about dismantling the Yeti model before it calls forth another of the creatures.

Lethbridge-Stewart has formulated a two-pronged plan for recovering the TARDIS. He and his men will go above ground to reach Covent Garden via Neal Street. Arnold, Lane, and Evans will take the trolley and go through the tunnels to reach it. Together, they should be able to find and recover the police box. The plan is understood, but not the purpose. Blake particularly is perplexed, but the Colonel will not give details. The police box is important, that's all he needs to know.

Captain Knight is ordered to stay behind to guard Anne, the Doctor, and his friends, a job that does not please him. The slight against him is clear.

In the lab, the Doctor has completed work on the model and now turns his attention to the fungus sample. With heavy gloves on, he prepares to open the tin. However, he is stopped by the arrival of Jamie who announces the departure of the troops for Covent Garden. The Doctor thinks this whole mission an exercise in futility, but he clearly can't stop them. All he can do is continue his work.

Putting the others at a safe distance, the Doctor gingerly opens the tin. To his utter shock, the tin is empty! Someone has done away with the sample. He immediately suspects Evans.

Evans is with Arnold at the main door, ready to take off. The cowardly Evans seems to be trying to weasel out of the trip, but Arnold won't have any of his innocent "I'm only a driver" act. Evans is here now and must do as he's told. One attempt to leave the tunnels and Arnold will have him for breakfast. Lane announces that the trolley is ready and they're off.

Above ground, all is going well. The streets are deserted and the mist seems to be holding off for the moment. Lethbridge-Stewart and his party are making good time. Ten more minutes and they should be at Covent Garden station.

With the soldiers gone, there is nothing the Doctor can do about Evans. They will have to question him thoroughly if and when he returns. The Doctor turns his mind back to the problem of the control box and tells Captain Knight that they need more transistors and circuits. Their stocks are inadequate and they must have more. The Doctor suggests going above-ground to try and find them.

Knight initially rejects this idea as too dangerous but the Doctor persists. Anne joins in, exploiting the Captain's fondness for her, and he eventually agrees. He and the Doctor will go, but Anne, Jamie, and Victoria will stay behind, firmly locked into the HQ. Jamie is none too happy about being left behind.

Arnold and his party have reached the wall of fungus outside Covent Garden and try to figure out what to do. They must hurry if they are to meet up with the Colonel and Arnold has a very dangerous idea. They must get the trolley through the mist and there's no gradient to the tracks. Someone will have to push the trolley through. He digs out gas masks and looks for a volunteer to help out.

Evans refuses, thinking Arnold is insane. Lane at first balks too, but then decides to do his duty. He must help Staff Arnold. They tie a rope to the trolley and leave it with Evans. If there's any sign of trouble, Evans is to pull them back to safety. Glad to be left behind, Evans agrees.

Once they are ready, Arnold and Lane begin pushing the trolley ahead of them, disappearing into the glowing fungus. Evans watches as the rope plays out.

Shortly, the fungus becomes more active, pulsing and glowing more brightly. A terrifying scream issues from inside the mass, followed by a second. Evans is paralysed with fear for a moment and then begins hauling back the rope. The trolley appears and clears the fungus.

There is one body on the trolley - Lane. He is dead, his respirator gone and his body covered with webbing. There is no sign of Arnold. Evans is traumatised, gazing into the mass of fungus in sheer disbelief. Where is Staff Arnold?

Lethbridge-Stewart and his men arrive at Covent Garden only to find their way to the station blocked by Yeti. They dive for cover as the Yeti approach, hemming them in. Gunfire erupts and the battle is joined. As always, the bullets have no effect on the robot Yeti. The gunfire continues, followed by several grenade explosions, but all to no avail. The Yeti are approaching relentlessly.

Several men are killed as they try to escape around the creatures. More bullets and grenades fly but the Yeti are unharmed. The Colonel spots a route of escape via a nearby warehouse and orders the men to get out of it. He uses a bazooka round to cover their escape. Several men are killed with web guns before they can make it out.

Also on the surface, the Doctor and Knight are looting an electronics shop for the spares they need. In the distance, they can hear the gunfire. Knight is very nervous. The Doctor heads for the back of the shop to find the last piece he needs. As Knight waits, he is horrified to hear a strange bleeping noise. Two Yeti burst through the door. Knight shouts a warning to the Doctor and tries to hold the creatures back with gunfire. They do not stop and soon he is under attack.

Knight is killed by the fierce creatures. The Doctor watches in horror, waiting for them to come after him. Surprisingly, they simply turn and leave the shop, their mission completed. The Doctor examines Knight's body and finds what he is looking for in one of the man's pockets - a Yeti model. Sadly, the Doctor returns to HQ underground.

The Doctor explains to Jamie, Victoria, and Anne what has happened. Anne is especially saddened over Knight's death, thinking that perhaps he stole the model. But the Doctor assures her that it was planted on him, deliberately placed to bring the Yeti to him. Evans has also returned to HQ and related his story as well. Suspicion again falls on him and he becomes angry. The Doctor tries to calm them all down, knowing that accusations will get them nowhere.

There is still one Yeti model missing. Where can it be?

Inside the warehouse, the battle between Yeti and soldiers continues. There is no further retreat and no way to stop the creatures. The soldiers are killed relentlessly. Colonel Lethbridge-Stewart continues shooting as long as his ammo holds out. He watches helplessly as Corporal Blake is killed.

Seeing a break between the creatures, the Colonel takes advantage and races for his life. He is the only one to survive.

In the lab, the Doctor dismantles the model Yeti. They are safe now. He and Anne decide to get to work on the control unit using the new spares he has obtained. Jamie and Victoria examine the Yeti model, wondering it could have gotten into Knight's pocket. Jamie suspects Chorley, even though he's been gone for quite some time.

They are all surprised when Lethbridge-Stewart returns, haggard and worn. He is angry at his failure and the death of the men, slumping down into a chair. He tells them what happened, comparing notes with Evans. All of the men are gone now, except them. Even Captain Knight is dead.

In the background, a soft bleeping sound issues. It takes them some time to notice it as the Colonel despairs of ever defeating the Yeti and the Intelligence. The Doctor is first to hear it and he knows immediately what it is: the last Yeti model is here in the room with them.

The Doctor springs into action, searching hard for it. The Colonel says he's heard the noise off and on all day and the Doctor knows - it is in his pockets. Not quite understanding, the Colonel is slow to react but eventually he turns out his pockets, revealing the final missing model. The Doctor tells the shocked man what the model is for: it brings the Yeti!

There is general consternation in the laboratory as everyone tries to make sense of what is happening. It appears that Professor Travers is working with the Yeti. Anne tries to go to him but the Doctor holds her back. They must listen to what he has to say.

Travers speaks in a hissing, whispering voice. It is a parody of his own, not unlike that of the lama Padmasambhva in Tibet when he was taken over by the Intelligence. Travers' voice tells the others that it is the Intelligence speaking through him. It has taken over Travers and is now ready to explain its purpose to them. The Intelligence tells the Doctor that he defeated it in Tibet, but now he has fallen into the trap which it has so carefully set.

The Doctor cannot believe the Intelligence has done all this simply for revenge and he is right. The Intelligence explains that it has observed the Doctor in his travels through time and space and has determined that his mind surpasses all other creatures. It has invented a machine that will drain all of the Doctor's knowledge and experience for itself. The Doctor will be left alive with a blank mind, like that of a newborn.

The Doctor asks what will happen if he refuses to give his mind to the Intelligence and it tells him that it will use the machine on some lesser creatures...many lesser creatures. Including Jamie and Victoria. The Doctor believes this threat and considers it seriously, especially when the Intelligence tells him he must submit willingly. If he does so, the Intelligence promises to let the others go free, unharmed, including Travers himself. The Intelligence says he is only a tool for communications and has no other value. Travers has not aided the Intelligence in this endeavour as it has "many other human hands" at its command.

The Doctor seizes on this information and tries to find out who its allies are. This angers the Intelligence and Travers moves forward to grab Victoria. It clearly must "guide" the Doctor's thoughts in this matter. Jamie tries to jump forward and help Victoria but the Doctor inexplicably holds him back. If the Doctor willingly submits his mind to the Intelligence, Victoria will be released unharmed. He has 20 minutes to decide. Travers leaves with Victoria and the Yeti.

Jamie struggles to get loose from the Doctor, angry that he has been stopped from helping Victoria, but the Doctor says he doesn't stand a chance. Colonel Lethbridge-Stewart agrees and bars the lad's way to the door. They can't just fight out of anger. They must come up with a plan. Jamie, angry, pushes past him and throws open the door. As expected, there is a Yeti just outside on guard. It roars and Jamie quickly closes the door. They are trapped.

The Doctor assures Jamie that Victoria will be safe for the moment. Without her, the Intelligence has nothing to bargain with and it needs to ensure the Doctor's cooperation. The same is true of Travers. The Doctor works hard to reassure his friends whilst Evans quietly addresses the Colonel. He suggests handing over the Doctor to the Intelligence if it will go away and leave them in peace. The Colonel sees this for the cowardly gesture that it is and rejects it with one baleful glance.

Travers roughly drags Victoria through the underground tunnels to its own headquarters. One Yeti accompanies them. Victoria tries to complain about the pain she is causing him but he is blank-eyed, under the complete control of the Intelligence.

The Colonel tries to assess their strategy, hindered by Evans' insistence on the Doctor giving himself up. Jamie is very angry, as is the Colonel. The Doctor reassures them all that he will give himself up if he can't think of some way to stop the Intelligence. He won't put the others at risk for himself. Jamie protests but the Doctor silences him. If the worst happens, Jamie must find and rescue Victoria and the two of them must look after him. If what the Intelligence says is true, he will be left with the mind of a newborn and will have to be taken care of... until he "grows up".

During this exchange, Evans has been listening at the door. Suddenly he opens it. To their surprise, there is no Yeti outside. He thought he had heard it lumber off. Lethbridge-Stewart, Evans, and Jamie go off to search the HQ, to make sure it's gone. The Doctor and Anne are left to get on with their work.

Anne watches the Doctor curiously, not certain why he's at the centre of all this. She can't imagine he's seriously planning to give himself up, but it is true. If he can't find a solution. He hopes it won't come to that. She is starting to despair a bit, noting that they've got less than 20 minutes to come up with a way to stop the Yeti. The Doctor says that's all the more reason to get right to work. The control box is their only hope and they must get it working.

The search has yielded nothing. HQ is empty. Clearly that Yeti was left as a sort of rear guard to allow Travers to get away with Victoria. However, Jamie is thinking ahead. He is certain that they are heading south, the only direction still clear of the fungus. If they can get out of the tunnels and go overland, they could get ahead of Travers and take them by surprise. The Colonel is sceptical and says so. Evans is scared and tries to weasel out of the whole enterprise. Jamie, disgusted, decides to go on his own. Lethbridge-Stewart, realising that there is at least a chance of success, agrees to go along. Evans will be left behind to guard the Doctor and Anne.

The Colonel goes off, warning Evans not to take any chances. Not surprisingly, Evans is not planning on it!

The Doctor and Anne have progressed quickly on the control box, the Doctor finding a novel way of connecting several of the circuits to allow for automatic frequency variations. Anne is impressed. The Doctor sets her to work completing the task while he turns his attention to the control sphere.

Jamie and Lethbridge-Stewart have gone to the surface door, not far from the main entrance, ready to try and get out. They both fear that there might be fungus on the other side and brace themselves to open it. It is very quiet on the other side so they think they are in the clear. However, when they open the door, they find they are mistaken. A mass of fungus, glowing and pulsing, oozes out toward them. They both push on the door, trying to force the fungus back, but it is too strong. They cannot get the door closed.

Lethbridge-Stewart spots a fire door just inside the HQ and sends Jamie to unhitch it. If they can get that closed before the fungus gets to it, they can at least hold it there. The Colonel uses all his strength to hold the door long enough for Jamie to get to the fire door. He just about manages, finally abandoning the effort and racing for the fire door. The fungus spills out in a great glowing mass.

The Doctor has reassembled the control sphere. It seems to be working but it's not picking up any signals from the Intelligence. Odd. He tries one last thing - giving the sphere one great thump - and suddenly it comes to life, bleeping away. He is very pleased with himself. Anne is pleased too, but her part of the work is going too slowly for her liking. The Doctor starts to go and help her but must break off when the sphere begins to move of its own accord, responding to the signals. He must keep watch over it to keep it from rolling away, although he is delighted at the response.

Jamie and the Colonel burst in and report their failure. They have stopped the fungus at the fire door, but it is now in the HQ. The Doctor suspected as much, knowing that the Intelligence would try to hem them in here. They can only hope the fire door will hold. Their only hope is the experiment on which the Doctor and Anne are working.

The Doctor tries to explain the plan to control a sphere using the box, but Jamie and Lethbridge-Stewart don't understand. It is only in the testing stage and the Doctor cannot even say conclusively that it will work. Lethbridge-Stewart finds this news underwhelming and is sceptical that they will achieve anything at all. Anne suggests that he go away and leave them to it and the Colonel does so, taking Jamie with him. Anne and the Doctor continue their feverish work.

Lethbridge-Stewart leads Jamie to the operations room to look at the progress of the fungus. They are startled when they enter to find Evans pointing a gun at them both. He looks grimly serious. To their surprise, he says that he has decided that one of them is in league with the Intelligence. Jamie insists it's Chorley, which doesn't surprise Evans very much. Of course he would try to deflect suspicion.

Lethbridge-Stewart is not amused by all of this. He and Jamie are going out into the tunnels and Evans will not try to stop them. He orders Evans to join the Doctor and Anne but Evans refuses. He says that this position is better "tactically". Lethbridge-Stewart scoffs at this coward's idea of "tactics" and he and Jamie push past Evans and out into the tunnels.

Travers has taken Victoria to the Piccadilly station and now waits motionless and zombie-like on the platform. Victoria is still unable to break his grasp on her wrists and begs to be released. Suddenly, the voice of the Intelligence issues from somewhere, telling Travers to let her go. Victoria tries to work out where the voice is coming from... and who it is coming from. But she is unable to. Travers is released from the Intelligence's control and he slumps to the floor. Victoria goes to help him.

Travers is OK, but a bit dazed. Victoria tries to get him to rest but he is determined to get back to HQ and help the Doctor. He thinks they can get past the Yeti guard if they are careful. It appears to be dormant anyway.

Travers gets to his feet and starts to lead the way quietly along the platform. But he was wrong. As they approach, the creatures comes to life and bars their way. The creatures gives out its blood-curdling roar and Victoria screams.

At last, the Doctor and Anne are ready for their first test of the control box. The sphere is bleeping away, still responding to signals from the Intelligence, and the Doctor activates the box. Nothing changes, even though the box is at full power. Anne fears they have failed but the Doctor tries one last thing. He moves closer to the sphere. Suddenly it stops bleeping and the Doctor is able to make it roll back toward him. It works! However, it only works at very close range, which could be quite a problem.

Now that they know they can stop a sphere from moving, the Doctor would like to adapt the box and allow them to control a Yeti sphere by verbal command. It is a tricky operation and they have only 12 minutes left. They must hurry.

Jamie and Lethbridge-Stewart reach a junction in the tunnels. Lethbridge-Stewart decides to go on, choosing one of the turnings. However, Jamie hangs back a bit, seeming suspicious all of a sudden. He admits that he is still thinking of what Evans said. One of them is working for the Intelligence and it might be the Colonel. He is afraid of walking into a trap.

The Colonel tries to assure him that he's not a traitor but when Jamie still seems sceptical, he simply presses on down the tunnel. Jamie hesitates and then follows. Something on the ground catches his eye - Victoria's handkerchief. They are on the right track and Jamie forgets all his doubts. He presses on.

Victoria reassures Travers that his daughter is fine and that she and the Doctor are working hard to finish the work to control a Yeti. Suddenly Travers stops speaking, hearing a noise from the tunnels. It is Staff Sergeant Arnold, beaten and disheveled but very much alive. Victoria had told Travers of the death of Lane in the fungus and the loss of Arnold. Travers is surprised but delighted to see him.

Arnold approaches along the rail bed, out of sight of the Yeti. He gets close enough to speak with Travers. There is no time for explanations. Travers tells him to get to HQ and warn the Doctor - tell him where they are. Without a word, Arnold agrees and sneaks off back down the tunnel.

Victoria thinks this is not enough. They should try to escape with him. Travers does not think this will work, not with the Yeti guarding them. Arnold is their only hope.

In ops, Evans is stunned to see a control sphere rolling toward him. The nervous little man leaps onto his chair in panic, pointing his rifle at the device. The Doctor hurries in and stops him from shooting. He then stops the sphere by voice command through a microphone. They have done it! He demonstrates their control for a sceptical Evans.

Evans can't see what good this "toy" will do them, but the Doctor assures him that once it is inside a Yeti, they will be able to control the creature by voice command. It will be a powerful ally. The problem, of course, is getting it inside a Yeti. Evans is appalled at the dangerous plan and wants nothing to do with it. The Doctor and Anne will just have to do it themselves then.

Arnold finally makes contact with Jamie and Lethbridge-Stewart in the tunnel. He is considerably worse for wear now and collapses at their feet. He explains that he blacked out on the trolley and remembers nothing until he came to in the tunnels. He is heading back to HQ to tell the Doctor about Victoria and Travers. Jamie is excited and wishes to go ahead and look for them, but Lethbridge-Stewart manages to get him to come with them. They should go back together - it's safer that way. At least they know now where to find them when they're ready.

At Piccadilly, Travers realises that the Doctor's 20 minutes are nearly up. As if in response to this comment, two Yeti come toward them on the platform. They are herded into the station and Victoria becomes very nervous. Travers tries to calm her, hoping against hope that the Doctor will find some answer to save them all.

The Colonel and the others return to HQ to find Evans hiding in ops. His face is guilty when he realises who he was hiding from. He is also very concerned when he sees Arnold still alive. He is sure he was dead. Arnold and the Colonel badger Evans into telling them where the Doctor and Anne have gone. Warren Street, he thinks, trying to find a Yeti. Warren Street is one of the few stations still free of the fungus, but it is approaching. They must hurry.

Arnold stays behind and Evans is detailed to dress his wounds. Jamie and Lethbridge-Stewart hurry back out into the tunnels.

In the tunnel, the Doctor and Anne are face to face with a wall of fungus. They cannot go any further. The two scientists appraise the fungus, the Doctor wondering whether it's mutating. However, they decide not to investigate any further and turn to go back. To their horror, a Yeti is right behind them. They are trapped.

The Doctor asks Anne for the control box, only to be told that she thought he had it. The Doctor frantically searches his pockets as the creature advances. He finds it as it is nearly upon them. It raises its arm to strike but freezes as the Doctor activates the control box. Anne lets out her held breath in relief. He really waited until the last minute that time.

Anne holds the box whilst the Doctor approaches the Yeti. He removes its control sphere and trades it for the one that he and Anne have modified. It is time for the test.

The Doctor speaks into the small microphone, ordering the creature to turn around. To his great joy, it does so. They have been completely successful and can now control a Yeti. Because of their modifications, the voice control should work over quite a distance. They now have a chance against the Intelligence. They move off into the tunnel, making sure not to forget their new pet, whom the Doctor dubs "Fred".

Evans finishes dressing Arnold's wounds, pleased with his fine work. When he is done, Evans goes to return the supplies to the store room, only to return a second later with a look of terror on his face. He cannot speak and can only drag Arnold out into the corridor to see what is wrong.

Arnold is horrified to see the wall of the HQ bulging inward under tremendous pressure. Something is trying to get in. The two men are frozen in panic for a second until Arnold urges Evans to run. The two men race for the exit as the wall gives way.

Staff Sergeant Arnold and Private Evans race into the tunnels ahead of the fungus that has engulfed their HQ. Arnold knows they must try to reach the others and warn them what has happened. He is shocked when Evans' cowardice is in full view and he refuses to go. Arnold tries to reason with him about his duty as a solider in the Army and then tries to badger him into obeying. Nothing works and Evans races off into the tunnels in the opposite direction. Arnold vows to get him for his desertion, but first he has a job to do.

The Doctor and Anne walk through another section of tunnel, followed by the Yeti which they now control. The Doctor, however, is worried. He is still concerned that someone in their group is working for the Intelligence so they decide to tell no one of the Yeti that they control, even though they fear that the Intelligence already knows what has happened.

The Doctor orders the creature to stay where it is for 90 seconds, and then resume acting on orders from the Intelligence until told otherwise. The creatures indicates understanding by a roar and then shuts down. The Doctor and Anne hurry off.

Shortly, they run into Jamie and Colonel Lethbridge-Stewart, who report fungus at Warren Street station. Jamie asks what they are doing down here and Anne just manages to stop the Doctor telling him with Lethbridge-Stewart standing there. He has been acting very strangely ever since he appeared on the scene and cannot be fully trusted. Anne tells him that they've had no luck with their "gadgets". A necessary lie.

The Doctor learns that Victoria and Travers are at Piccadilly station. He is suspicious when the Colonel says they are unharmed, wondering how he knows this, and the eyewitness account of Staff Arnold actually complicates matters. Arnold was supposed to be dead, swallowed up by the fungus. The Colonel can offer no explanation as to how Arnold survived and there's no time to pursue it. The Doctor's 20 minutes is up and they must get to HQ.

Jamie and Lethbridge-Stewart lead the way. Anne and the Doctor hang back, whispering between them. They must keep their secret for now. With some luck, they might be able to increase the range of their control box once they reach the lab.

Behind them, the Doctor's Yeti comes back to life. It is joined by two others and they move off down the tunnels, all acting on orders from the Intelligence.

Lethbridge-Stewart and the others run into Arnold in the darkness and he reports the destruction of HQ. He also notes the desertion of Evans with obvious disgust. There's little they can do and the group seems unsure of their next move. However, it is decided for them as the three Yeti arrive and surround them. Time's up.

Elsewhere in the tunnels, Evans wanders hopelessly. He hides as one Yeti passes, but he is caught unawares by a second creature behind the first. He tries to reason with the thing, his voice thick with fear. He is grabbed and dragged down the tunnel.

At a junction, the Yeti procession halts, and Arnold makes a decision to try and break free. As they start to move again, Lethbridge-Stewart causes a distraction by stumbling and Arnold is able to take off into one of the other tunnels. In the chaos, his disappearance is not noticed.

Victoria and Travers are led by Yeti into the ticket hall of the Piccadilly station. It is the central control point for the Intelligence. In the centre of the hall is a giant glass pyramid, much larger than the ones used by the Intelligence in Tibet. It is hollow and has an opening in one face. Inside is a chair. Travers is fascinated by it and tries to examine it. He is warned off by the roar of a Yeti.

Victoria sees a shadowy figure in an alcove and wonders if it is the Intelligence. They cannot tell and the movement is gone. Victoria realises that time is short and can only hope that the Doctor can find some way to stop the Intelligence. Travers despairs that it is too late. The Doctor will have to submit himself in order to save his friends.

The voice of the Intelligence booms out through the hall, telling Travers that he is right. The Doctor will soon be here to submit himself to his fate. The voice warns them both not to interfere, or else they will be destroyed. Travers despairs, blaming himself for all of this. If only he hadn't tampered with the control spheres, none of this would have happened. He is certain he's sacrificed all of them.

On the platform of the Piccadilly station, the Doctor and his party wait under Yeti guard. The Doctor plays his recorder, sitting off to one side with Jamie. The Doctor has finally told Jamie of the Yeti that he controls, knowing that he will need his friend's help. He says that he's still suspicious of Lethbridge-Stewart and they cannot tell him what is going on. Unfortunately, the Doctor has no way to tell which of the three Yeti is his and leaves Jamie the task of finding out. He gives Jamie the microphone and tells him to keep calling to the Yeti until he finds out which one responds.

To do this, Jamie will have to break away from the group of prisoners. The Doctor spies a small bin nearby and gets an idea...

Staff Arnold bumps into Harold Chorley in the tunnels, quite an unexpected arrival. He had completely forgotten about the mousy little journalist! Chorley says he's been wandering round the tunnels for ages all by himself, unable to get away even on the surface because of the Yeti. He then tried to get back to HQ but couldn't get back underground until he reached Piccadilly. Once there, he saw the pyramid and Victoria and Travers and all the Yeti. It was all he could do to escape from there.

Arnold is unsympathetic at first and Chorley apologises for his fear. Arnold is quite suspicious of him, wondering just how he managed to survive all the Yeti and the fungus and the mist. The insinuation is quite clear and Chorley is shocked. Arnold backs off his accusation and suggests that Chorley come along with him.

The prisoners sit and wait on the platform at Piccadilly station. Jamie is nowhere to be seen. Luckily, the Yeti have not noticed this yet. Anne asks why the Doctor doesn't use his control box to try and get them free of the Yeti, but he says that he must meet the Intelligence face to face. It is the only way to stop it. The Colonel joins them and awkwardly suggests that the Doctor give himself up, at least to safeguard Anne and Victoria and Professor Travers. The Doctor finds it odd that this military man would actually believe the Intelligence's promise to free them all unharmed if the Doctor surrenders.

The matter drops for the moment as more Yeti arrive, bearing Evans. He seems none the worse for wear, actually rather cheery. However, Lethbridge-Stewart has heard all about Evans' "exploits" from Arnold and it seems very like desertion to him. Evans says that is a total misrepresentation. He went off on his own on a desperate mission to save Travers and Victoria. Lucky for him, Arnold isn't around to dispute him.

As this conversation ends, there is an increase in activity with the Yeti. One moves forward and grabs the Doctor. It is time for him to go. However, the others are to be left here for the moment. The Doctor lets himself be dragged away, but he manages to shout a message to the others before he goes: when the Yeti come for them, don't struggle. Just go with them. Evans can't understand this, but Lethbridge-Stewart does. The Doctor really is going to give himself up.

The remaining Yeti come to round up the others.

The Doctor is led along a passageway by his Yeti escort. A second creature joins them, bearing a strange headset-device. As soon as the second Yeti gets close enough, the Doctor activates his control box. Both of the robots freeze. The Doctor, working quickly, takes the headset and makes a few adjustments before returning it to the Yeti. The whole enterprise takes only a matter of seconds.

The Doctor reactivates the creatures and the headset is placed on his head. The Yeti then lead him off down the passageway again.

In the ticket hall, Anne, Evans, and Lethbridge-Stewart join Travers and Victoria. Anne is delighted to see her father again, alive and well. Victoria inquires about the Doctor and Jamie but Anne is unable to give an answer.

Back on the platform, Jamie emerges from his hiding place into blessed silence. Using the small wireless microphone, Jamie begins calling to the Doctor's Yeti. After a moment, one of the creatures appears from the corridor, approaching Jamie. However, when Jamie orders it to raise its right arm, it does not obey. He backs away as the creature continues to approach, repeating the order. It roars ferociously. Clearly this is not the Doctor's Yeti after all!

The Doctor is brought into the ticket hall, led by the two Yeti. He seems very calm, especially contrasted with the fear emanating from Victoria and the others. He tells them there's nothing to worry about and says that everything's under control. Only Anne believes him. A Yeti roars and the Doctor's friends start. He tries again to reassure them that he's perfectly all right, despite the strange headset he wears.

The voice of the Intelligence rasps out through the ticket hall, thanking the Doctor for being so cooperative. Lethbridge-Stewart challenges the Intelligence to show itself and suddenly Harold Chorley comes stumbling through the passage, looking like death. Everyone suspects he is the culprit, but he desperately denies it. Behind him is the real voice of the Intelligence.

To everyone's horror, they see Staff Sergeant Arnold emerge into the light, walking calmly and wearing a headset like the Doctor's. His Yorkshire accent is gone, as is the military manner. He speaks with the calm voice of the Intelligence. The Intelligence tells them that Arnold is dead, his body occupied to give the Intelligence a form from which to work. And it is now time to get to work. Anne realises in the callous manner of the Intelligence that all its promises to let the others go once the Doctor had submitted were lies. She had been naïve and trusting.

Arnold turns and looks back at the tunnel as another Yeti arrives, bearing the last member of the party. Jamie. Victoria is glad to see him alive and well but is saddened to know that he was likely their last hope. The Intelligence is eager to finish its work and orders Jamie to join the others. Then a Yeti grabs him firmly around the neck, in order to ensure the Doctor's "complete cooperation". Disobey and Jamie dies. However, the Doctor refuses to submit unless Jamie is released. There is a moment of stalemate and then the Intelligence relents and the Yeti releases its grip.

The Doctor agrees to do as the Intelligence says and he is ordered into the pyramid machine.

The Doctor gets inside the glass structure and sits. Arnold adjusts several controls to prepare for transference of the Doctor's mind. Soon all his knowledge will be absorbed by the Great Intelligence. His knowledge of the past will help to shape the future of Earth. The Doctor urges the Intelligence to get on with it, saying that he just wants it over with. He seems quite resigned to his fate. The Intelligence is somewhat suspicious though, reminding him that unless he submits completely, the transference will be of no value and any attempt to hinder the process will result in swift punishment for all of his friends.

The Doctor understands and the Intelligence is ready to begin the process. Suddenly, Jamie leaps into action. He produces the microphone and shouts to the Doctor's controlled Yeti to attack. The creature responds to the order and chaos erupts in the ticket hall. The creature sets upon the other Yeti, knocking them away from the pyramid. Then Jamie orders it to attack Arnold. It does so.

Jamie and Lethbridge-Stewart race to the pyramid and attempt to drag the Doctor clear. In an act of utter redemption, Evans joins them. To their astonishment, the Doctor resists them, trying to remain seated in the pyramid. A Yeti joins the fray against them and pushes them away. The Doctor remains seated. However, Chorley joins in and soon the Yeti is out of the way. Jamie, Anne, and Travers then try again to free the Doctor. He continues to fight, shouting for them to leave him alone. He becomes more and more angry but he cannot resist the combined forces of all those trying to "help". He is dragged clear of the pyramid.

Jamie pulls the headset from him and tosses it back into the pyramid machine. It explodes mightily, knocking everyone to the floor, destroying the pyramid and banishing the Intelligence from Earth once again. The Yeti control spheres all explode and the robot creatures fall to the ground. Smoke fills the hall as the echoes of the explosions die away.

Everyone picks themselves off and dusts themselves down. Evans, for one, is glad to see the end of the menace. However, the Doctor does not share his enthusiasm. In fact, he is livid. He harangues them all for interfering. They have "ruined everything". Jamie is stunned, certain that they've won against the Intelligence, but the Doctor assures him he is wrong. He explains the sabotage that he had performed on the headset. He had crossed the wires on it and instead of the Intelligence draining his mind, he would have drained the Intelligence if the procedure had gone on. Now, the Intelligence is still around, at full strength. Its contact with Earth has been severed but it is still out in space, free to try to attack Earth again whenever it pleased.

The Doctor points to the body of Arnold on the floor of the hall. His face is blackened, his already dead body destroyed when the Intelligence was defeated. Everyone is horrified at the twisted expression in his dead eyes.

The Doctor insists that he has failed and is very sad indeed. However, first Travers, then Anne, then Lethbridge-Stewart tells him that he is a hero. He's managed a great victory against the Intelligence. As they speak, the Doctor seems to brighten. As long as they all think he's a hero...

Chorley joins in the praise but begins to push it too far. He tells the Doctor that he will make him a household world, a national figure for his part in all this. There will be TV appearances, a press conference... As the overzealous journalist continues his litany, the Doctor starts to get worried. He begins backing away, along with Jamie and Victoria. He wants no part of hero worship.

The Doctor bids a quick goodbye to all his friends and then beats a hasty retreat back down into the station. Travers is sad to see him go once again, but he understands. They are off to Covent Garden, presumably to find their mysterious "TARDIS".

Chorley wants more information on this time-space machine the Doctor mentioned but Travers won't answer. He's got work to do. He leaves Anne to handle the explanations, a task she loathes. Unfortunately, she cannot get away from the persistent little man.

The Doctor and his companions traverse the tunnels of the Underground, now completely lost on their way to Covent Garden. Unfortunately, all the tunnels look alike to them. The Doctor is in a hurry although Jamie can't understand why. The Intelligence is gone and there should be no more fungus in the tunnels. The Doctor agrees, but he is very worried that the trains might start running again soon.