The Doctor thought his interrogator might have given up on him, but he should have known he’d be back for more. It’s not as though he’s actually refusing to answer his questions, the truth is he can’t tell him anything - even though he knows what will happen. The Doctor is bored with the physical violence, pain and torture, but his interrogator points out there are other methods he could use besides the purely physical. He may have to introduce the Doctor to Mr Twyst, his expert on such matters. In fact, he’s been looking forward to it. The Doctor assures him that he really can’t help as he’s lost his memory, but that doesn’t convince the interrogator. He likes a challenge.

Tessa Waylund calls out to Marcus, urging him to stop hiding. At first her voice echoes emptily down the corridor, but after a while Marcus calls out from the shadows and begs her to go away. She realises he’s terrified and tells him the others have also been looking for him. She’s concerned for his welfare and assures him that Latch stills thinks they can escape if they work together as a team. He refuses to move, confident that it can’t find him down here. But he’s wrong. Something is approaching and Marcus knows he’s next! They both run in terror and he urges her to leave him and find the others…

The TARDIS materialises and the Doctor, Charley and C’rizz find themselves inside a dark empty building. They’re obviously in the wrong place as they were expecting to join the heaving crowds attending the Festival of Ghana, but this is a cold metallic structure with no light and no windows. The instruments definitely say they’re on Earth, but the place seems deserted. They slide open a door and are immediately hit by the stench of human sweat and fear. The Doctor switches on a torch and a voice shouts out to them to stay away. The man tells them something is inside his head and he starts convulsing. He tells them his name is Marcus, then he screams in agony as the top of his skull completely explodes. They examine the body and notice something odd about the man’s eyes - it’s more than just fear they can see, it’s almost as though the eyes are empty. He was wearing ill-fitting overalls and didn’t carry any form of ID, but the Doctor guesses there must be friends or family around who’d want to know what happened to him.

Jane Thirgood explores the long, dark corridors, calling out for her friend. Gorden Latch appears and tells her there’s no sign of the others. She thinks Tessa is alright, but neither of them have made any contact with Marcus and they conclude he must be dead. They’re being picked off, one by one, but there has to be a chance for them to survive. It’s just a case of finding it before they’re killed. A door slides open and Tessa joins them. She explains that she left Marcus hiding, but it might already have been too late for him. She appears to have given up all hope, but Latch is determined to find a way out. If Tessa won’t help them, then at least she can stop hindering them. He wants to find the person responsible for this and kill them, but Tessa thinks they’re all beyond held now.

The interrogator is still not convinced by the Doctor’s claims of amnesia. The Doctor assures him his mind is a complete blank and he has no idea how he arrived there. The interrogator accuses him of being a Psike - a psychic or telepath - but the Doctor strongly denies this as he’s certain he’d have noticed by now even if he has lost his memory. The interrogator reveals that psychic powers won’t work in here because the walls are lined with psychic energy suppressants. He asks the Doctor what it feels like to be suddenly reduced to the level of a normal human, but he can’t answer. He volunteers to submit to hypnotic memory regression, but his interrogator has something more simple in mind, a reminder of his recent past. The door opens and C’rizz is dragged in, relieved to find that the Doctor is still alive. Unfortunately the Doctor genuinely doesn’t recognise him and is sure they’ve never met before. C’rizz urges his friend to remember him and Charley, but the interrogator is not interested in questioning C’rizz any further. He’s obviously not human and therefore cannot be a Psike, but it occurs to him that he may be able to persuade the Doctor to remember things by torturing C’rizz in front of him. The Doctor promises to tell him anything he wants to hear, but when C’rizz makes a casual reference to Latch, the interrogator is shocked to discover that the man is still alive. The Doctor is resigned to the fact that there‘s nothing he can do, regardless of what punishment is given to the man claiming to be his friend.

Tessa tells Latch that she last saw Marcus hiding under a stairwell on one of the ancillary walkways on the lower levels. He was scared and could sense something was coming after him. Jane accuses her of running away, but she swears they both just panicked and ran in different directions. They can guess what’s happened to him, especially as they’ve lost all trace of him, as though he’s been blanked out of their minds. Jane is the telepathy expert and she should have a better idea than anyone, but when she tries to make contact with Marcus, there’s nothing there. However, she can sense someone else…a stranger, a doctor, here in the Cube. That means there’s someone new in there with them - and he’s telepathic!

The Doctor, Charley and C’rizz hear the metal clang of a door opening or closing somewhere in the distance. His companions want to go back to the TARDIS, and although the Doctor is surprised that they’re afraid of spooky noises, C’rizz reminds him that they’ve just witnessed someone having their skull turned inside out. The Doctor is intrigued by the strange acoustics of the building and wants to remain, but his friends persuade him to make a discreet exit just this once. They hurry back to where they think the ship is, but are confused by the strange architectural layout and find themselves facing a locked door that they’re sure wasn’t there before. They sense something is gaining on them and just as the Doctor opens the door with his sonic screwdriver, he suddenly vanishes completely. Inside the room, Charley and C’rizz discover the TARDIS has also disappeared.

Using her telepathic ability, Jane leads Latch towards a trace left behind from where the strangers came in. They don’t understand what could have happened as it’s not possible for anyone to teleport in. As they realise Tessa is no longer with them, their attention is diverted by some sort of psychic disturbance, possibly caused by the stranger they’re looking for. Latch starts to sense something too, just on the edge of ESP. He’s frustrated by this place as it makes them practically blind. They stumble across Marcus’s body and discover it is just like the others. It’s now more imperative than ever that they find this doctor - if he could get in, then he must be able to find a way out too.

Charley and C’rizz desperately try to shut the metal door behind them to protect themselves from whatever is approaching. They can’t believe they’ve lost both the Doctor and the TARDIS and they wonder whether he left in the ship, thinking they were right behind him. They hear strange noises from behind the door and realise that whatever it is, it isn’t going to give up. The door bursts open and the two travellers are forced to flee. At that moment Jane and Latch arrive and order Charley and C’rizz to follow them before it’s too late.

The interrogator implores the Doctor not to give up so easily. He doesn’t care that this prisoner is tired, he insists on knowing the full story of what happened inside the Cube, and specifically how he got out. He wants to find out what the Doctor knows about the thing that attacked him - did he see it and how did he get away? The interrogator offers to bring out C’rizz again, but warns him he’s quite a mess. Desperate to stop them hurting his friend any more, the Doctor convinces himself that he must have seen the thing and that he must have a mental block that’s stopping him from remembering. It’s there in his mind, but all he can picture is some sort of worm, turning and twisting in the dark, blood-red and blind. The interrogator realises that he did see it. The Doctor’s done well, but still he needs more answers. He needs to know who is left alive in there…

Charley demands answers from Jane and Latch. Before Charley and C’rizz can introduce themselves, the telepaths are able to guess their names, but they can’t fathom out which Psike Team they could have come from. The travellers explain that they’re not part of any team and they were brought here by the Doctor. Jane is delighted to find she was right, but Latch believes they’re liars and insists they tell him the way out. Charley decides the conversation is getting a bit too confusing, so she wants to start again. However, they don’t have time to discuss things any more as they hear the sound of something approaching in the darkness and decide to keep moving to throw the ‘thing’ off their scent. If they can reach the upper level fast enough, they still might have a chance.

The Doctor wants to know why the interrogator is so interested in finding out about the man named Gorden Latch. He explains that he’s a very dangerous man, a criminal and murder who put the word ‘psycho’ into psychokinetic. He’s the leader of the Psikes and was one of the first people to be successfully converted. He’s a superb telekineticist and an absolutely lethal telepathic assassin. One thought is all it takes and the victim is dead, most likely by using telekinesis to cut off every electro-chemical reaction in the brain. It’s not a natural talent and the interrogator reveals that he made him like that. He refuses to explain to the Doctor why he would do such a thing. Instead, he demands to know whether Gorden Latch, Marcus Lenn, Jane Thirgood and Tessa Waylund are still alive. The name ‘Marcus’ triggers a memory in the Doctor’s mind and he recalls that something turned his head inside out. But everything else is still missing and the Doctor can almost feel the hole in his head where his knowledge, information and emotion used to be.

Charley, C’rizz, Gorden and Jane continue to flee through the strange metal corridors. The thing that’s chasing them can’t be far behind, but nowhere in the building appears to be safe. The only thing they can do is keep moving until the thing either loses them or gives up. Jane is amazed that the new arrivals don’t know what it is that they’re escaping from or where they are, and she tells them they’re in the Cube. C’rizz realises their new colleagues have been reading their minds, but Jane reveals that she can’t read anything now that C’rizz is deliberately suppressing their thoughts. Charley is curious about this as she didn’t know the Eutermesan was telepathic and he admits there’s a lot she doesn’t know about him.

The interrogator realises the Doctor has not only encountered the brain-worm, he’s actually been damaged by it. It must be loose in the Cube, and he wants to know what it is and why it’s there. At the first sign of trouble in there, the surveillance system shut down and the Doctor is now his only source of information. The Doctor slowly starts to remember and becomes distressed. He says it scratched the inside of his mind, but for some reason it didn’t kill him.

C’rizz has become separated from the rest of the group and they have no choice but to assume he’s already dead. However, the Eutermesan is still alive - although he appears to be tied up. He calls out desperately to anyone else who can hear him, and a man’s voice responds. The newcomer shines a torch in C’rizz’s face and asks him how he got there. He’s already drawn the conclusion that he must be connected to the other stranger they found outside the Cube earlier, and C’rizz realises he’s referring to the Doctor. The Eutermesan demands to be untied, but the man wants the answers to a few questions first. He wants to know how he was able to escape from the prison…but unfortunately C’rizz doesn’t know.

Charley wants Jane and Latch to go back with her to help C‘rizz, but they insist it’s too dangerous. They don’t really know what the brain-worm is, but it’s deadly and it’s in here with them. Charley remembers the man they found by the TARDIS and the others realise it must have been Marcus. He was only 20 years old - their youngest recruit - and was full of energy and optimism until he came to the Cube. Latch reveals they were all soldiers, used by the Army for any specialist mission where psychic powers might be useful. These missions included eavesdropping on the enemy, reconnaissance, teleport incursions, even telekinetic assassinations. They were developed by Eryk Rawden, the scientist who found a way to artificially develop ESP to engineer volunteers with psi powers for use on the battlefield. But now the war is over and it was a complete victory for their side, thanks to them. The normal soldiers were discharged but the Psychic Soldiers can’t be released, not even to see their families and children. The authorities are frightened of them - they can read any mind, open any door, even kill someone with a single thought. They’re no longer regarded as brave soldiers, fighting for their world, but have been reclassified as criminals and killers. The Cube was designed as a prison to hold all the telepaths and they’re serving a death sentence in there right now.

The interrogator tells the Doctor he’s done well and should get a reward, but the Doctor knows exactly what kind of place this is. The Cube is a prison - a terrible, sad, wicked, inhuman prison. But he’s escaped from prisons before and he’ll do so again if he can. The interrogator says the information he needs is still buried inside the Doctor’s mind and he intends to dig it out, piece by piece if he has to. He couldn’t care less if it hurts. The Doctor has no hope, no rights and no chance of escape.

Charley asks Jane and Latch what happened to the rest of their comrades. All the other Psikes are dead - some of them were given surgical treatment, but the doctors didn’t really know what they were doing. They tried to reverse the techniques that were used to increase their natural psychic ability in order to reset their brain patterns to normal, but the effect was only temporary. Whatever they did to make them telepathic in the first place, the result was permanent. Many of those who underwent Rawden’s surgery died from massive psychic shock and when the treatment was stopped, the survivors were locked inside the Cube and left to rot. They can’t use their powers to escape because the Cube is built from a special metal that nullifies psychic ability and any powers that remain are severely weakened. Now that Marcus is dead, there are only three of them left, including Tessa who is the weak link in their chain. She’s a loner, or a loser, depending on your point of view. Some say she was the most powerful Psike ever made, but Latch disputes this. He never liked her because she refused to be part of the team and preferred to work alone, but her speciality was teleportation and the others always thought she was their best chance of escape. They hear a noise in the distance and decide to set off again to find the Doctor and C’rizz.

The interrogator tells the Doctor they have a machine that can re-write brainwaves, which was used originally to create the Psychic Soldiers. He concedes this was probably a mistake, but the war called for desperate measures and his decision was not taken lightly. In fact, the interrogator can’t understand why he and the Doctor aren’t friends. After all, they’re both perceptive, intelligent men, strong-willed and determined. In many ways they’re very alike. For the first time, the Doctor is genuinely disturbed.

Latch and Jane call for Tessa and her voice responds from the darkness. She greets Charley, having been able to read her mind even from a distance, and she invites them to join her inside a very cramped room. Charley bangs her head, but fortunately Tessa was the group’s medic and she uses her special powers to take away the bump. She also reveals to Charley that Latch and Jane brought her here as their hostage! They plan to use her to help them escape, but Charley insists that although she’s willing to help, she won’t make a good hostage as no one outside will care enough about her. Tessa was also the group’s infiltration expert in the old days and no one was better than her at teletransportation, but now she’s intrigued by the image of the TARDIS in Charley’s thoughts. She can sense that it’s a time machine and that only the Doctor knows how to operate it. Latch insists that Charley’s friends have been killed by the brain-worm, and Tessa suspects he may be right as she can’t sense the thoughts of the Doctor or C’rizz anywhere.

The Doctor asks how the brainwave machine works and although the interrogator claims not to be a technical expert, he knows it has something to do with brain cell augmentation. The Doctor is pondering whether the machine, if it’s sophisticated enough, could be used to repair his own neural damage - but when the interrogator reveals that brain damage wasn’t uncommon during his earlier experiments, the Doctor hurriedly changes the subject. The interrogator decides this might be an appropriate time to introduce the Doctor to Garth Twyst, his coercion specialist. His friend C’rizz has a tough exoskeleton that made normal methods of physical brutality ineffective, so Mr Twyst has had to be more inventive. The interrogator hints that it might be worth trying the brainwave machine on C’rizz instead.

Charley refuses to accept that the Doctor and C’rizz are dead and says it’s much more likely they’re simply not in the Cube any more. Latch insists there isn’t a way out, and when she reminds him that he’s supposed to be the one that never gives up, he becomes frustrated because the material in the walls is pressing down on his mind all the time. She tells him the Doctor is their only hope but when she tries to go looking for him, both Latch and Jane agree that it’s too dangerous for her to wander around the building with the brain-worm on the loose. However, they also accept that nowhere in the Cube is safe any more, so eventually they’re all persuaded that they might as well die trying to do something.

C’rizz wakes up and begs Twyst not to continue with the torture. He tells the Eutermesan not to be silly - there’s still plenty more to come so he should save his strength. The next stage will be to reactive his nerve-endings by re-opening some old wounds. C’rizz refuses to tell him anything, but the torturer explains that he hasn’t actually asked anything. In fact, there’s nothing he could tell him that would be of the slightest interest. Twyst is just about the begin work with the electric saw when the interrogator, Eryk Rawden, enters, accompanied by the Doctor. Twyst welcomes them, but the Doctor is horrified by what he sees and snatches the saw from the torturer’s grip. Twyst explains that they’re in the Psychotronic Adjustment Unit and he’s engaged in important scientific research. The Doctor accuses him of being a butcher and requests some painkillers for his injured friend. Rawden tells Twyst what they have planned for the brainwave machine and he agrees to demonstrate the equipment. All they need is a volunteer…

The Doctor screams out in agony and Rawden orders Twyst to increase the power. However, the machine is already operating at full power - so why isn’t it working? Believing it’s burned out the Doctor’s nervous system, they reluctantly prepare to switch off the machine, but when they hear their patient begging them to stop, Rawden decides to patch in all the other systems, even if it risks causing an overload. The lights dim and an alarm sounds. Twyst goes to adjust the equipment, then screams out and freezes like a statue. The Doctor looks over to Rawden and the same happens to him. Now fully revived, the Doctor jumps off the operating table. He tells C’rizz that he temporarily separated his conscious from his subconscious and placed the two scientists in psychic paralyses. The machine turned him into a Psike and he’s using telekinesis to hold the scientists prisoner. Although the machine had been re-programmed to delete psychic power, he used his own brainwaves to reverse the polarity from the inside. For a short while at least, he has massively increased his own telepathic ability. As they leave, Rawden struggles to fight against the psychic force field and warns the Doctor there is no escape.

Latch leads the others back up to the upper level, but Charley is devastated when there’s no sign of the Doctor or C’rizz. He’s convinced that the brain-worm has killed them. They hear an approaching noise and Latch suddenly becomes convinced that Charley herself is somehow leading the brain-worm towards them, just like C’rizz did. He tells the others they must leave and he forbids Charley from joining them. Jane apologises, but reluctantly she agrees to stick with Latch and they abandon their new friend to her fate.

The Doctor half-carries the badly injured C’rizz away from the laboratory and the Eutermesan finally accepts that the Doctor genuinely can’t remember him and wasn’t bluffing as he’d originally thought. They know the telekinetic force field must be fading by now, so they hurry as Rawden and Twyst can’t be far behind. Indeed, as they speak, the two scientists are fighting against their paralysis… C’rizz asks the Doctor to leave him but receives a lecture about the differences between a rescue attempt and an escape attempt. The Doctor can remember the way out as he was faking unconsciousness when they first brought him in, and they eventually arrive at the main exit chamber. They see the TARDIS, but the Doctor doesn’t recognise it. He’s amazed when C’rizz explains that the blue box is their home and they travel through time and space in it. C’rizz is starting to suffer from his blood loss and the Doctor admits that he feels responsible because Rawden tortured him purely as a means of getting him to talk.

They search for the chamber’s power supply, but as the Doctor looks for his sonic screwdriver, he realises his pockets have been completed emptied. Instead, he gets to work prising a nearby hatch off its hinges to expose some wires. Neither of them are sure how they got to the control centre from the Cube, or where they currently are in relation to it, but the Doctor guesses the centre is probably a self-contained unit positioned on top of the Cube itself. They presumably got here by teletransportation, the transference of matter by psychic power, which prompts C’rizz to suggest that the Doctor uses his new powers to trip the lock of the door in the same way he would have done if he still had his sonic screwdriver. It works and they climb back into the Cube - the Doctor is determined to get his memories back and the only way to do so is for him to have a word with the brain-worm!

Rawden urges Twyst to keep up as they can’t afford to lose the Doctor now. They realise he’s trying to get back into the Cube as he wants the same thing Rawden is after - they’re both desperate for answers and they can only get them from the brain-worm. They discover the Doctor has fused the controls of the exit, trapping them on the outside but sealing the Doctor and his friends on the inside.

Latch is furious with himself for the way he’s behaved. He feels guilty for leaving Charley alone and he admits to Jane that he panicked. He realises they’re just running around like rats in a barrel waiting to die. The creature is going to kill them all and maybe, he thinks, they actually deserve it! Jane assures him that everyone who’s survived so far owes everything to him and he can’t let them give up now.

Charley starts to panic as she flees from the brain-worm and ends up in a dead end. Just then, the Doctor appears and asks if she’s Charley. She’s delighted to see both him and C’rizz, and as the Doctor leads them to safety, she helps to carry the injured Eutermesan. They make their way through the maze of metal corridors until they think they’re in the clear. The Doctor explains that he’s lost his memory and they’re in a prison run by a man named Rawden, who’s unpleasant, short-tempered, paranoid and prone to violent outbursts. In return, Charley tells him the brain-worm is hunting telepaths, but he corrects her and adds that it actually hunts anything from which it can absorb brain energy. But he needs to see it again in order to get his memories back.

He asks Charley and C’rizz to think hard about whether they’ve actually seen the brain-worm in a physical form and they realise they can’t describe it, even though it was right in front of them on two occasions. He tells them the creature is quite literally incomprehensible, they can’t see it in the ordinary way, but only in the same way that they see an idea or see someone else’s point of view. They hear the brain-worm approaching and agree that they can’t just keep running forever. The Doctor wants to get medical treatment for C’rizz fairly urgently and they help to carry him, but soon realise they’re not going to get away in time, so the Doctor stops and openly challenges the brain-worm. The Doctor is attacked and when the creature leaves, he realises that another part of his mind is now missing. Something has been torn out of his head, but because he has a very large and complex mind he can’t be too sure yet what’s been taken. They wonder why the creature suddenly stopped its attack, and the Doctor suggests asking Tessa - who happens to be standing right next to them!

Jane asks Latch if he felt a twinge, a movement, something stirring deep inside his mind? He can’t feel anything and Jane suddenly realises it’s Tessa she can sense inside her head. But there’s something else…and they realise the Doctor has returned to the Cube. Charley introduces the Doctor to Tessa and she leads them to her personal hideaway. The Doctor guesses it was Tessa who removed the TARDIS from the prison and moved it outside as she’s the only one with the power to teleport something of that size. She admits that it was her and that it would take more than a few ESP suppressors to clip her wings! She was also able to home in on their brainwaves, which is how she found them so quickly. Tessa is able to pick out every thought in people’s heads - even the Doctor’s - and hold it up to the light. She knows, for example, that the Doctor’s main concern at the moment is C’rizz’s internal injuries, so he asks whether she can use her healing powers to restore him to health. She’ll need his help as she only has the psychic powers, not the knowledge of Eutermesan anatomy. Although the Doctor doesn’t remember anything, he still has an instinctive appreciation of alien physiognomy.

He therefore asks if he can make telepathic contact with her, even though it will be very dangerous for him. She can already sense that he has deep dark secrets - but is he willing to share them with her in order to save his friend’s life…? She knows that even as they speak he is trying to throw up barriers to seal off parts of his mind by thinking of trivial things, like reciting poetry, scientific formulas, football scores. But it isn’t working. She answers the question he hasn’t dared to ask - yes, she is as dangerous as he fears! That’s the way Rawden made her. She is the brain-worm! The Doctor can sense it hiding inside her head, cold and crawling…

At first Charley tries to apologise to Tessa for the Doctor’s behaviour but he becomes angry at her inability to see the truth. Tessa was the first to be treated after the war and the brain-worm lives inside her. The machine was faulty, so it didn’t remove her psychic powers, it doubled them, perhaps even tripled them. The powers in her mind grew and mutated, absorbing her own brainwaves and becoming a separate living entity. She killed Marcus when she cornered him in the lower levels, but it can also get out and roam the Cube look for more victims, before slithering back inside her head.

Charley rushes to check on the Doctor, but he seems to be uninjured although he can feel the brain-worm in his head. This is ‘almost totally’ what he expected and he believes he’s been quite remarkably brilliant even by his own standards. He’s managed to trap the powerful telepathic energy being inside his own mind and he’s confident he will be more than a match for it. Although it’ll be a while before it takes effect, he should also find his knowledge and memories will start returning, but at the moment his recipe for perfect custard has got mixed up with Fermat’s Last Theorem. Tessa takes the opportunity to heal C’rizz using telekinesis and vital information gleaned from the Doctor’s mind. When she finishes, she tells them she was disturbed by some dark she found places in C’rizz’s mind, but before she can elaborate the Eutermesan revives. The Doctor prepares to lead the group out of the Cube. She doesn’t remember helping the Doctor earlier to escape the Cube using teletransportation, and he explains that it was really the brain-worm, working through her subconscious. As they move off, C’rizz asks Tessa what she saw in his mind and when she denies seeing anything, he reminds her that he is moderately telepathic too so he knows she’s lying.

Latch tends to Jane, who feels weak after making mental connection with the Doctor and Tessa. Latch is curious about the fact that the only person who didn’t think the Doctor was dead was Charley. He thinks they may have been looking at the situation from the wrong perspective. What if there never was an attack on the Doctor? Perhaps he faked it and left the Cube the same way he came in - which would mean he is working for Rawden. This would explain how he appeared here in the first place and how he seems to be able to come and go at will. Convinced by his own argument, he swears to kill the Doctor.

Tessa asks the Doctor why she was unable to control the brain-worm, but he reminds her that despite her psychic powers, she’s still only human. He plans to remove the creature from his mind using the brainwave machine but they need to escape first. Unfortunately it was the brain-worm that allowed them to teleport out last time and he can hardly ask it to help now that he’s made it a prisoner. Just as he’s claiming that nothing else can go wrong, they find themselves confronted by Rawden and Twyst, who’ve entered the Cube using the Doctor’s own sonic screwdriver. They overheard their discussion and know that the brain-worm is being held inside the Doctor’s mind. Twyst grabs Charley and threatens to blow her head off unless the group co-operate. The Doctor warns them that while they delay, the brain-worm is struggling to get out, scratching and gnawing for a way out. He can’t hold it forever, but Rawden refuses to let him destroy the creature. He sees it as a powerful weapon that can be used in future wars. Rawden orders Twyst to shoot Charley and for a moment, the Doctor panics. This is all the brain-worm needs to find a weak point in his mind and escape, killing Twyst on the way. Now the creature is free again and is most likely hiding in someone else’s mind - but there’s no way of telling whose.

The group begin to suspect each other, not knowing which of them is the new host for the brain-worm. Rawden accuses the Doctor of lying about keeping the creature prisoner in his head, but he points out that it was their own actions which caused the current dilemma. Rawden begins to panic and starts accusing the others randomly. They each deny that the creature is inside them, but the Doctor knows that it can hide inside the subconscious without the host even realising it. He thinks it’s unlikely that the brain-worm would have left his mind, killed Twyst, and then returned to the same place … but he concedes that it is a possibility. There’s only one way to find out - the Doctor and Charley play a game of children’s counting rhymes to establish who is “it”, but to Charley’s surprise she ends up pointing to herself. No one else can believe they’re serious, but the Doctor theorises that it could have been her subconscious at work. Rawden demands that they kill her, but the Doctor restrains him and throws away his weapon. By doing so, he may have saved Rawden’s life as the brain-worm will certainly kill anyone who points a gun at it’s hiding place. The Doctor insists that everyone be treated as innocent until proven guilty, but Tessa says she’s starting to sense terrible murderous thoughts. She starts to scream in agony and then falls to the floor, dead. The Doctor realises the brain-worm recognised her as a threat as she was about to reveal where it was, so it killed her. During the distraction, Rawden runs off into the darkness. It’s clear he must be heading for the exit and he still has the sonic screwdriver. The others race to catch up and the Doctor is now convinced that Rawden himself is the new host of the brain-worm! If it escapes from the Cube, there will be nothing to stop it getting to the outside world.

As Rawden races through the corridors in desperation, he’s suddenly grabbed by Latch and Jane. For a moment Latch considers killing him on the spot, but then they realise Rawden must be heading for the exit. He tells them Tessa was the brain-worm all along, but now that she’s dead it’s hiding out in someone else’s mind like a slug under a stone. They look into his mind and pick up on Rawden’s belief that the creature is inside Charley. He offers to show them the way out if they let him live, but Jane can sense that he’s lying. Latch doesn’t care and the only thing he’s interested in is getting out of the Cube. He starts to speak in a strange monotone voice and Jane realises that the brain-worm is now in Latch’s head! She cries out in agony and dies. The brain-worm, now speaking through Latch’s voice, repeats over and over again that all it wants is to get out of here…

The Doctor tells the others that once the brain-worm has killed everyone in the Cube, it intends to get out and kill every living thing on the outside. He has no idea how they’re going to stop it and is hoping they’ll get extra time. C’rizz is unfamiliar with this term and the Doctor explains the history of the 2005 European Cup Final in which Liverpool was 3-0 down at half-time against AC Milan and everything looked hopeless. He was there when Liverpool scored three times in the second half and went on to win the match in extra time. The point of his story is that they must never give up, even when the odds against them are overwhelming.

The brain-worm/Latch demands that Rawden shows it the way out. Just then, the others arrive and find Jane’s body. The Doctor admits that he was obviously wrong about Rawden being the host, and the brain-worm must have jumped out of his mind and straight into Latch. Rawden offers to show the creature the way out in return for his life, but the Doctor insists they must all remain trapped inside the Cube and die. This is the only way that the world outside can remain safe. Rawden again offers to lead the brain-worm/Latch towards the exit, but the Doctor warns him he’ll be dead five seconds after he’s opened the door. The Doctor says they’re past extra time and they’re now playing in a penalty shoot-out. They will live or die by what happens next, but it depends on everyone trusting him. Charley and C’rizz agree immediately, and Rawden reluctantly falls into line.

The Doctor reveals that the brain-worm is actually trapped inside Latch because he’s the ultimate psychic and has a mind like a steel trap. Charley wonders what this means for Latch himself, but the answer is obvious - he can never have his freedom. He can never to leave the Cube, and when Rawden opens the hatch that leads to the outside world, the others will walk out and he will have to stay behind, totally alone. Barely able to walk, Latch turns and moves back down the corridor, giving the others the opportunity they need to escape. But just before they do so, Latch uses his own telepathic assassination technique to kill Rawden. The hatch seals behind the Doctor, Charley and C’rizz. Sadly, they realise that sooner or later Latch will die and the brain-worm will be trapped on its own. Forever.