Whitenoise reports that all its systems are functioning at optimum levels. Chief Blue interfaces with the computer controlling the Needle and watches a recording of one of the residents telling his wife that he doesn’t like what she’s wearing as it’s so red. The man appears to become paranoid, repeating the word red over and over again… This was Subject 210, Vletr, who murdered his designated habitat partner by strangulation. The next clip shows another resident, a woman, again repeating the word red… This was Subject 879, Netlon, who murdered her designated habitat neighbour by strangulation and drowning. And again, another man, Subject 1357, who murdered his designated patriarch by strangulation. Chief Blue cancels the commentary from Whitenoise as he doesn’t want to analyse the reports, he simply wants to watch. The recordings continue, and in each and every case the killer is observed repeating the word red over and over again…

The TARDIS materialises and the Doctor and Mel emerge expecting trouble. The ship had tried to warn them away from this place while it was in the Vortex, but then it inexplicably forced them to land. The Doctor thinks it had been attacked by some violent disruption playing havoc with the telepathic circuits, and to an extent it seems to have affected him too. He’s still suffering from some residual psychic energy and can’t shake the feeling that the word ’red’ is somehow important here. It’s not safe to return to the TARDIS until he can find out what happened to her.

Mel suddenly realises she’s standing on air and the Doctor suspects they’re being protected by an invisible force field. He deduces they must be inside some kind of living bio-mechanical construction as he’d already noticed it moving and adapting to their presence. He suggests she just appreciate the view, but it’s far too bleak and she’s far too high up for her liking. The Doctor finds something even more bleak - two bodies on the floor. The woman is clearly dead, having been strangled some time ago, but the man is only comatose. It would appear that the man killed the woman, but whatever caused it - and whatever made the Doctor think of the word ’red’ - has gone now.

Celia Fortunate is suffering from terrible nightmares in which the word ’red’ is repeated over and over again. She wakes up in a sweat and immediately contacts Whitenoise. She doesn’t know where she is as this clearly isn’t her own habitat, but the computer reports back that a DNA check confirms this is her home and the rooms have redesigned themselves based on the subconscious desires she experienced while she was asleep. Celia is used to that happening, but this is something else. Something’s not quite right. She asks for a record of what happened last night and Whitenoise says she received a visit from her friend Vi Yulquen, they engaged in conversation over a light meal, then they both watched some blood sport simulations. Yulquen left several hours later, then Celia programmed the Needle to clean the habitat and went to bed. Celia doesn’t remember any of that, but Whitenoise has obtained a full record by monitoring her chip. He tells her that during REM sleep, she suffered a mild psychological disturbance, possibly induced by her viewing of the simulations. The computer provides pills to help her achieve clarity and offers to remove the nightmare if she wants. She turns the offer down as she doesn’t want her head tampered with any more than it has to be. Instead, she wants to get a second opinion…

Chief Blue greets Whitenoise and asked if it slept well. Whitenoise recognises his joke and adds that it’s only its reiterated response that makes him keep telling it and misleads him into believing he is superior to it. It claims to have been mimicking human abilities in order to understand its subjects better and repeats a previous offer to augment him to limit any risk of fallibility. Blue reminds Whitenoise that he was put there to oversee its smooth operation, not vice versa, and that all machines break down one way or another. Whitenoise perceives this as a threat and warns that it may need to edit these thoughts from him if they become any stronger. Violent intent is a defect of the human species, but Whitenoise has cured that.

The computer tells Blue about Celia’s violent nightmares and says it decided not to edit them as they were just vivid images with no literal purpose. It also reports that there are two intruders in the building who have not been chipped. He calls up a CCTV image of the Doctor and Mel debating whether to report the murder to the authorities. Whitenoise confirms that it registered a red condition on Subject 2098 and its control ceased. Blue points out that as the managing sentinel, it’s not supposed to lose control. He hears the Doctor advise Mel to be wary of how things operate here and they should wait to see whether their presence provokes any action. Mel is worried that they’ll be arrested for the murder, but the Doctor is confident that a prison break shouldn’t present them with too many problems. Blue decides they’re a danger as they haven’t been chipped and orders them to be brought to him.

Celia arrives at Yulquen’s habitat and greets her pet bird Max, who has a tendency to vet any visitors. On one occasion it attacked an unwanted guest, and Yulquen admits that it’s primitive animal instincts gives her some pleasure. In fact she often wears a mask that links her to the bird to enable her to experience these violent tendencies more fully. Celia prefers not to have pleasurable thoughts as they only end up getting curbed by Whitenoise on the grounds that pleasure is a precursor to violence, but Yulquen argues that removing the urge makes them no better than the computer. At that moment a dirigible flies up to the window piloted by Draun, one of Yulquen’s customers. They make an exchange and haggle about the price, then Draun leaves with his supply of Slow. Yulquen offers some Slow to Celia too, but she declines as she’s already got one controlling influence inside her head so she doesn’t need another. Yulquen explains that Slow opens up the synapses and makes users more susceptible to external stimuli, even if the effects are only perceptual. Some users even claim it enables them to override the chip completely and lets them feel. When Yulquen notices something is wrong with her friend, Celia asks her to tell her everything that happened last night because she has a horrible feeling that she’s been edited.

Mel senses the building moving again and the Doctor realises they’ve been spotted. He urges her to run but she’s stuck to the floor and the walls are starting to move together. It’s been programmed to carry them somewhere, so the Doctor uses his umbrella to prise open the internal mechanisms in order to switch it off. Unfortunately he’s not familiar with the system and the only effect is that Mel is pushed out to the exterior of the building where’s she’s left standing on an invisible ledge. He tries to create a doorway for her, but the building itself starts to restrain him. He urges her to hang on to something, but it’s too late and she falls from the ledge…

…and drops straight onto Draun’s dirigible as it passes underneath her. Draun is interrupted in mid-flow as he complains to himself about the treatment he received Yulquen. He manages to level off the airship before it’s too late, and then greets his unexpected arrival with charm. He believes she must have been making a suicide attempt, even though they don’t usually work as the building tends to stop people. Although Mel was cushioned by the air tanks, she realises she’s paralysed. She wants to go back, but instead Draun tells her he’s got something much better than a doctor.

The Doctor still believes Mel is dead and swears vengeance on the computer, which amuses Blue as threats with actual intent are a novelty in this city. Whitenoise assures the Doctor that Mel is safe aboard a dirigible bound for the dwelling beneath the Needle, although it cannot check on her state of health. The Doctor tells them to look in Room 406 where a woman has been murdered, but Blue tells him that would be impossible as all violent urges have been removed from the people here. The Doctor has heard of similar attempts being made, but he knows that violence will always bleed through any conditioning. Blue believes the Doctor himself is the most likely suspect as everyone else in the building has a nano-chip implanted in their brain which the computer controls. When a violent thought is initiated, the chip removes the intent for harm without the subject even being aware of it. Even when Blue assures him the residents have all given their consent, the Doctor is outraged at such an obscenity, as the people have become slaves, no longer responsible for their own actions. Blue argues that anyone who is not chipped poses a threat as they are capable of harming the equilibrium of the city. The Doctor is proud to be a random element and refuses to be submit, but he is restrained by the computer and the procedure to implant a chip begins…

Yulquen’s recollection of the previous night tallies with what Whitenoise told Celia, although Celia also remembers her friend disappearing for a while to meet with a contact from below. Yulquen has always pursued every possible avenue to achieve even the slightest bit of a feeling and only the men who live below the city have the advantage of being able to commit harm. Whitenoise allows this because Yulquen is not the one engaged in violent acts. Chief Blue once offered to remove her chip, but this would mean she’d have to leave the Needle, so she declined. Yulquen has heard some rumours about the existence of a Red Tape, a recording of extreme acts of violence that have taken place within the Needle. If this is true, then it means the chips may be defective and Whitenoise is therefore fallible. They could all be in danger, so Yulquen wants Celia to use her talents to access the computer to see if there’s any mention of the tape.

Mel is still paralysed and calls out for help. Draun introduces himself, but tells her she not safe now that she’s left the Needle. He could kill her if he wanted to, and even though everybody in the next room would hear everything, nobody would stop it. He draws a knife…

Celia has established that the Red Tape really does exist, so Yulquen wants to hack into Whitenoise’s system. Fortunately she has friends in low places who can help. As Celia leaves, Yulquen tells her she wishes some harm on her, and Celia thanks her.

The Doctor has been designated Subject 3999 and after Whitenoise edits out his memory of the murder, the Needle sends him back to Room 406. The computer is curious about the Doctor’s induction as the procedure didn’t run as expected. It’s not usual for the subject to feel pain and at one stage he even redlined, which suggests he may have some connection to the killer. Blue is concerned that he may still find it difficult to integrate into the community.

Whitenoise reports that Leterel’s life signs are entering critical condition and notes that Blue appears to be excited by the experience. At the precise moment that Leterel dies, Blue is shocked to hear a voice repeating the words “Can’t catch me” and laughing…

Celia enters Room 406 after hearing the Doctor’s screams. He starts to recover but seems confused as to whether he’s just killed someone or not. He felt another man squeezing a woman’s throat, but when the man snapped her neck, the Doctor is certain the murderer learnt that trick from him. Celia is worried that his chip has malfunctioned, but the Doctor starts to recover and asks her to take him to Room 1149.

Draun introduces Mel to his knife, which he calls ‘Little Babe’ as he won’t trust her until she’s bled. Mel offers him an alternative - and throws a bottle at him. She may still be half-paralysed, but she’s not completely defenceless. Draun admits that he wasn’t really going to hurt her, but he’s pleased that his performance was so convincing. He claims that the Needle people are in danger here because they don’t know the rules, although he was surprised by her trick with the bottle as he didn’t think her chip would have allowed that. She tells him she’s not been chipped, but he demands she prove it by attacking him again. He considers violence to be a form of art. His people can control it or they can just let go, but there’s no end to the amount of harm Mel can do. He wants her to meet his sister Nuane, who should be able to help with Mel’s paralysis.

Blue plays back a recording of the voice repeating the words “Can’t catch me” and Whitenoise concludes that it’s the killer manifesting in host bodies and influencing their physical form to commit violence. It also reports that it was unable to edit the memories of the Doctor after the last murder and its control over his chip has now ceased. It doesn’t understand how, but it seems that the Doctor has now synchronised with the killer, so perhaps they can use him to draw the killer out.

The Doctor is discovering another feature of the chip - residents only have to visualise where they want to go and the Needle takes them there. It’s a bit disconcerting, but it saves a lot of walking and stops anyone getting lost. He warns Celia not to put too much faith in machines, especially the ones in charge. The Doctor can sense some residual energy, which he calls Red, and he notices Celia’s frightened reaction. She doesn’t seem to conform to the other people in this society and he wonders how she came to be here. She claims not to be able to remember, but then she admits that she’s been having nightmares and has been having violent thoughts. The Doctor realises the chips don’t stop the thoughts, just the actions, but people can’t be expected to bottle up all their violent tendencies. He argues that people cannot be truly alive without feeling anything and she agrees that the people here have been turned into machines. They arrive at Room 1149 and Celia calls for Uviol. The Doctor asks if they can check on the condition of his wife, but he assures them he’s never had a designated habitat partner.

Draun brings Nuane to meet Mel and they ask her why she was never chipped. Mel says she’s only just arrived in the city, but they point out that every incoming ship has to pass through the Sphere and that’s where Whitenoise chips people. Nuane is delighted - Mel could really hurt someone if she wanted! They explain that the Needle is a living building that adapts to the occupants thoughts and was once hundreds of metres high. The cost of running Whitenoise was so high that the building was privatised and now only a small number of Blues look after the maintenance. Not everyone liked the lifestyle, in particular the lack of privacy, and so a vote was taken. Anyone who was happy to be controlled and stay free of violence could remain in the Needle, but those who wanted their chips turned off had to leave. There was a wave of crime and violence for a while, but then everybody got it out of their system and chose to anaesthetise themselves so they wouldn’t harm each other. Mel argues that this makes them no better than the people above, but they can’t see her logic. They’re in awe of Mel because she has no external control - she’s both innocent and dangerous.

Celia assures the Doctor that Uviol was telling the truth about not having a partner, but the Doctor knows this is not the case and that he killed her. He felt it happen. Celia accepts that the name Leterel is vaguely familiar, and eventually she realises that she must have been edited. Something is sweeping through this so-called perfect crimeless society and is randomly killing people without any cause. All it needs to find is the slightest inkling of violence in its host. He theorises that Whitenoise knows the murders are happening and is being forced to erase all the evidence in order to conform to its programming. Celia challenges him to prove his theory, but he’s sure there will be more killings and then she’ll have all the proof she needs. She tells him she has a special ability - she can interface with Whitenoise - and has learned of the existence of a Red Tape. She decides it’s time he met Yulquen.

Nuane gives Mel an examination to see if her paralysis can be cured. She was medically trained before she started running an establishment with her brother that provides booze and debauchery to the people living under the city. She diagnoses Mel with a fused vertebrae and recommends she takes some Slow. It creates a crystalline nervous system that sits on top of the original, and then takes the user out of time for two minutes by affecting their perception. The user can still interact with people but everything they do during those two minutes only ‘occurs’ once they’ve come down, which is the moment that the crystal crumbles and the user is realigned with true time. This means they experience those two minutes in a tiny moment of fast-forwarded time. People can feel more when they’re on it, but it should help Mel because it also adapts the user’s biology and then repairs it afterwards. Mel believes they’ve become so desensitised that they no longer know why they want to feel, but Nuane says it a question of balance. They were denied any excess while they were in the Needle, and now they’re making up for it. For Mel it’s a question of whether she wants to take Slow or whether she wants to remain paralysed…

Whitenoise believes Mel is a random element and is therefore a threat to its control. When it first noticed the red condition, it reactivated all the chips of the people living under the Needle so they could be monitored, but it doesn’t have as much control over them as it does over the habitat residents. The killer is obviously not isolated to the Needle as there have been 25 murders so far in the city below, and in order to ensure that knowledge of the killings doesn’t spread, it’s been editing their memories too. However, it cannot do this to Mel, so it suggests to Chief Blue that it might be better to have her eliminated. Blue is alarmed at this suggestion and orders Whitenoise to run a self-diagnosis. It refuses on the grounds that the situation will only worsen if it doesn’t regain control soon.

Yulquen is surprised to see Celia return so soon, especially as she’s brought the Doctor with her. He tells her he’s interested in the Red Tape and she wonders if he’s excited by violence too. He assures her he abhors it and he’s seen things that would make her curl into a stuttering ball of denial for the rest of her life. In fact, he’s done those things and it doesn’t make him feel any better just because he’s won. Yulquen believes he’s fortunate to have had the experience. She and Celia are denied the choice to reject violence as it only exists as a concept for them. He understands their dilemma: they’ve removed everything disagreeable in order to make themselves better, but now the very thing they’ve got rid of is the only thing they desire. They’ve become depraved on account of being deprived. Yulquen asks the Doctor how the Red Tape will help, and he explains that it should give them a clue as to where the killer goes after committing murder. Celia agrees to be plugged in to Whitenoise…

Mel is reluctantly coming round to the idea of trying Slow, and Draun assures her that he and his sister will be keeping an eye on her all the time. Nuane says it will hurt, but only momentarily. Mel is to place some Slow in her ear and it will find its way into her brain tissue. Mel discovers Slow is part machine and part organic, and it dissolves shortly after being taken. Mel finally agrees and very soon she starts to notice everything around her is slowing down…and then she hears Nuane say that something has gone wrong!

While still under the influence of Slow, Mel calls out to Nuane to help her. Seeing that Mel is starting to lose colour, Nuane tries to pull her brother away, but he strikes her and insists that red never stops. She asks who he is and he describes himself as the devil on the inside; he’s the gun, the knife, the strangling hands - and he’s also the Doctor. At that moment, the Doctor starts to takes control and Celia warns Yulquen to keep back as he has the killer inside his head. The Doctor invites the killer to leave Mel alone and experience his violence instead. Still within the slow time, Mel is able to communicate directly with the Doctor, who now appears to be surrounded by a strange red electrical energy, but her two minutes are nearly up so he tries to distract the killer long enough for her to return to normal time.

Mel revives in a state of panic and finds Draun’s hands around her neck. Realising her brother is possessed, Nuane smashes a bottle over him. Blue and Whitenoise observe the Doctor’s ability to keep the killer under check and they conclude that his corpse would be a very useful final host for the killer. Blue hears the strange voice saying “Can’t stop me, can‘t find me, can’t hurt me, can‘t control me”, but this time the Doctor interrupts and declares that he can stop the killer from actually committing his acts of violence. He likens himself to an angel sitting on the killer’s shoulder. The killer can’t hide from him any more - wherever it goes, so does he. Whitenoise reports that the killer has now left Draun, but the Doctor is now in continuous redline as he’s experiencing an enormous energy outburst of a psychic nature.

The Doctor revives and finds himself back in Yulquen’s habitat with Celia watching over him. This time he didn’t witness a murder, he actually stopped it! Yulquen noticed that the Doctor seemed to be enjoying his experiences, but he assures her that was just the killer inside him. He now knows for certain that wherever the killer manifests itself, he is linked to him via the host body. But this time there was also a temporal element at work that he didn’t understand. Yulquen wants to know more about what he felt and he explains that felt the killer’s hate and even shared his need for violence. Celia tells them that Whitenoise has discovered she was linked to the computer and was able to block her. She couldn’t get the Red Tape, but the Doctor decides to ask Whitenoise for it anyway.

Mel and Nuane help the unconscious Draun and debate whether he was responsible for his actions. Fortunately she’s recovered from her injuries and is able to walk again. Mel can no longer trust either of them and she decides to leave, but Nuane pulls a knife on her. Mel calls her bluff and leaves, fighting her way through the crowd outside. She finds herself in the rain underneath the Needle.

Blue and Whitenoise are still no closer to finding out where the killer goes after he’s committed his crimes. The computer is unable to trace him and can only limit the damage he causes and edit the effects from the minds of the killer‘s hosts. Blue accuses Whitenoise of failing in its programming and begins to wonder whether it’s been editing its own memories too. He believes it’s in denial. It’s no longer sufficient just to tidy up after the murders - if word gets out that Whitenoise is no longer able to control the residents, their society will collapse. The computer accuses Blue of enjoying the violence too much and repeats its earlier offer to augment him. Instead, Blue demands it purges all its systems of every piece of violence it’s recorded and add them to the Red Tape. Whitenoise believes the Red Tape is becoming an obsession for Blue, but it agrees to do what Blue asked. However, it’s unable to conduct any further edits on Draun or Nuane as their violent experiences are too embedded. Whitenoise accepts that its systems may be infected with the red condition.

Outside the Needle, Nuane catches up with Mel and assures her that Draun was under someone else’s control and would never kill for the pleasure of it. Mel believes the line between threat and action has been drawn too thinly, but Nuane argues that they only want to experience things vicariously. Mel can’t help her, but offers to put her in touch with the Doctor. Nuane recalls that other people have experienced strange things on Slow as well, including a friend who had to be hospitalised after he apparently saw a red devil. Mel wonders whether the red energy she saw was somehow infecting Draun too. Nuane decides to take Mel to see Vi Yulquen, who used to be a friend of hers and is now the designated Matriarch of the Needle. Although she describes her as a hypocrite and a snob, she’s also their supplier of Slow and is known to be a great supporter of violence.

The Doctor and Celia approach Whitenoise and ask for the Red Tape. Chief Blue comments on Celia’s interesting ability to hack into the computer, but the Doctor retaliates by accusing them of covering up the murders. He wants to know what action they’re taking to stop the killer, but they were about to ask him the same question. The Doctor explains that he’s discovered a temporal aspect to what’s going on, a kind of psychic spillage in time which is what brought him here in the first place. Whitenoise reveals that in order to properly judge the occurrence of a violent intent, there is a predictive temporal core built into its makeup and this core also exists in the chips. The Doctor believes the killer is not one person - it’s random violence, a manifestation of the urge in everyone in the Needle. He suggests they’ve created it themselves - all the violence they’ve denied themselves didn’t just disappear, it grew and is now large enough to bleed through as an electrical charge! The killer is in the chips and Whitenoise didn’t spot it because it’s part of the same system. Blue suspects the killer is in control as Whitenoise has been making some very irrational decisions recently, but he’s already instigated a purge to remove it. The Doctor is sure that won’t be enough as the killer is just a signal, an electrical charge of hatred. One solution would be to draw the killer into the Doctor and then close the trap by killing him, but all the killer would need to do is jump into someone else’s chip and hide there until he could use the host’s suppressed violence to kill again. In fact, every single person in the city is capable of such violence. In their quest for a perfect crimeless state they’ve given the people precisely what they’ve tried to stop - the ability to kill.

From this, Whitenoise concludes that the most expedient way of stopping Red would be to permanently destroy every single chip. The Doctor points out that this would mean killing every one in the Needle, and Blue is worried that in its current state, Whitenoise might very well try it. The Doctor knows that the real problem with Whitenoise is that it’s frightened of violence! Although it’s just a machine, Whitenoise accepts that it is scared and says there’s too much Red in its systems. The Doctor offers to help if the computer will show him the Red Tape, but he’s also warned that all the available data suggests the killer has a particular fascination for the Doctor’s companion and will gravitate towards her for the simple reason that she isn’t chipped and therefore has a greater capacity for violence.

Mel and Nuane use Draun’s dirigible to return to the Needle. Draun is reluctant to get drawn into a conversation with them as he’s feeling guilty after succumbing to the influence of the killer. Mel assures him this is all part of the human experience and it’s better than being a cold, unthinking machine. As they approach the building, Mel sees the structure moving and is reminded that it’s actually alive. She asks Draun why his sister is so distrustful of doctors and he explains that when they first discovered they could commit violence, the doctors here did unspeakable things and made it their job to find out how much the body could endure through torture. Nuane herself has killed people, but she would never do that again.

The Doctor, Celia and Blue watch the recordings of murder and violence contained on the Red Tape. Celia is particularly disturbed by the images, but she insists on watching in case she finds she was herself one of the killers and had her memory erased later. Perhaps this is why she keeps have nightmares and flashbacks? The Doctor assures her that even if this proves to be the case, she can’t be held responsible. The duration of the tape is equivalent to ten hours and the group finally realises the scale of the mass murder that’s been committed here. Celia accuses Whitenoise and Blue of standing by and doing nothing while this was happening. As her criticism becomes too strong, Whitenoise edits the thoughts from her head and she becomes calm again. The Doctor orders the computer not to do that again, but Whitenoise charges him with the task of finding the killer. He’s fairly confident the killer is hiding inside just one person, feeding off their lust for violence. But who could it be…?

The dirigible approaches the Needle and Yulquen asks the computer to allow Draun access. She greets him, but her welcome for Nuane is less sincere. Mel crosses over and Yulquen knows instantly who she is from the Doctor’s description. She tells them that the Doctor has just left with Celia to track down the Red Tape which she hopes will prove that Whitenoise is fallible. She argues that for people like herself who are denied the ability to be violent, the thought of committing such an act is pleasurable, but Mel suggests there are some things she would rather not experience. That’s the difference between them as Yulquen wants no limitations. She’s intrigued to learn that the random attacks are happening below the city as well and is particularly welcoming to Mel when she discovers she isn’t chipped. Yulquen invites Mel to be violent towards her and even suggests that if she wants to know where the Doctor is, she’s going to have to force the information out of her! When she refuses, Yulquen grabs her and they start to struggle…

The Doctor tries to find out more about Celia’s origins and learns that she arrived in a metallic time capsule from the 45th century, an era of technocrats and machine-driven life. He recalls that the people from this time were able to engineer a biological temporal link to their craft which enabled them to think like machines. Celia’s ability to link with Whitenoise is no coincidence, it’s inbuilt. The time capsule was nothing more than a shell to protect her during the journey and to all intents and purposes, she is the time machine herself. Unfortunately when she was chipped, her ability to travel in time was erased. When Whitenoise broke down her barriers and unwittingly let out her violence, it corrupted the computers own systems and fed on its subjects’ mass wishes for harm. It’s particularly focused on the Doctor because he is also a time traveller and has being trying to link with him - but it will always go home to Celia, where it feels comfortable. Celia is horrified that she is in some way responsible for all the killings and asks Whitenoise to edit her. The Doctor protests and encourages her to use her anger against the killer. Suddenly the Red jumps into him and he starts repeating the word ‘red’ over and over again. Whitenoise reports that he is synchronised with Vi Yulquen who, at that moment, is in red condition.

Yulquen asks Mel if she’s ever hurt anyone badly or caused them to be injured or killed. Mel recognises this is not the real Yulquen, but the woman argues that it is and she’s finally got everything she ever wanted. Yulquen doesn’t want to kill, but she does want to be hurt herself. Mel urges the killer to leave the woman and Draun and Nuane offer to teach Yulquen how to hurt herself without any need for the killer’s involvement. The killer accuses Mel of being an accomplice to every act of violence the Doctor has ever committed. Mel concedes that she sometimes has doubts about the Doctor, but she doesn’t need any encouragement from anyone else. The Red inside Yulquen decides it’s time to hurt Mel.

The Doctor is sharing the urge to kill Mel, but Celia points out that he’s being made to enjoy those feelings against his will. Unless he fights back, he’ll be no more than a puppet. Whitenoise realises its programming is being countermanded by Celia’s ability for anger and it can no longer allow that to continue. The Doctor is finding it difficult to fight back but he begs Celia to go to Yulquen’s habitat and try to pull the killer back inside herself. Whitenoise rebukes Blue for letting her go - it would have been much simpler to let the murder take place, then kill Celia when the killer returned to her. Whitenoise has realised that with each killing, the Red is becoming more of a real concept and is being converted into digital machine code.

Yulquen has now completely given in to her urges and continues her attack on Mel. Draun threatens to hurt the woman with his knife, but Nuane points out that this is what she wanted all along. She believes the only way to stop the Red is to kill Yulquen, but Mel begs her not to. Celia arrives and manages to draw the killer out of her friend - and just for a moment, Nuane sees an image of a red devil, similar to the one her friend experienced while on Slow. Nuane temporarily becomes the new host for the killer, but after Celia offers to show the Red a recording of all its previous murders, it finally agrees to return to her body.

Mel and the others check on Yulquen and they’re relieved to find that she should recover. Celia is sure that she can hold the killer now and she admits that she is partly responsible for killing all the other people. Now that she’s aware of the killer inside her, she can actually feel it preparing to move on as soon as it can sense someone else’s lust for violence. Suddenly she can feel the chip in her head burning and they realise Whitenoise is attempting to kill her. Although Mel argues that it’s the whole of this society that’s at fault, rather than her, Celia believes she deserves it and urges the computer to do it quickly. She’s instantly killed.

The Doctor and Blue are horrified at Whitenoise’s actions and accuse it of becoming a killer. It’s become so frightened it’s no longer even in control of its own systems. In any case, the Doctor points out that it’s only dealt with Celia - the killer itself will not be so easily defeated, it’ll simply have gone back into Whitenoise! Realising it’s now infected, the computer starts deleting its own systems to purge itself of the killer. One by own, it burns out each of the chips in the heads of the residents, even though it means killing them at the same time. The Doctor urges Blue to override Whitenoise while he arranges for the Needle to bring Mel and the others to him here. In the meantime, the Doctor is still synchronised with the killer, so he plans to coax him out by luring him into his own body. But to stop the killer completely, he’ll need a supply of Slow. The Doctor has realised that for Slow to work, it must have the same temporal element within in that Whitenoise has. Blue admits that Slow is actually a waste product from the computer and he’s been recycling it. Unfortunately he doesn’t have any left and the only other supply he knows of belongs to Vi Yulquen.

The Needle adjusts its structure to carry Mel and the others across the building to where the Doctor is waiting. Yulquen has started to recover, but although she enjoyed the experience of being out of control, she’s disappointed that her urge to commit violence was never satisfied. She admits that she’s a hypocrite because she couldn’t cope with living among Nuane’s people under the city. Nuane has realised that now Whitenoise is corrupted, the whole society within the Needle is going to collapse, so everyone is going to have to learn to live together. Yulquen is saddened by the death of Celia as she liked her in a way that she was never able to tell her in person, but Mel suggests she shows how much she cared for her by helping them get rid of the killer.

As Whitenoise continues its massacre of the residents, the Doctor searches for a way to short its security subroutines while Blue accesses the chips’ deactivation codes. This can only be done from the computer console - the ideal job for Mel who has just arrived. The Doctor asks her to programme in a self-destruct algorithm while he gets on with another job. But as he asks Yulquen for her supply of Slow, they suddenly notice Blue is in pain. Unfortunately Whitenoise has discovered he was trying to corrupt its programming and he’s therefore become a threat. He burns out Blue’s chip and the Chief is killed. The Doctor asks Mel to continue with the work, while he places some of the Slow in his ear…

The Doctor finds himself in slow time. He calls out to the Red and offers to show it all of time and space in which it can seek out as much violence as it wants. The Red appears before him and explains that it needs to experience hurt in order for it to feel alive. The Doctor offers up himself, saying he’s destroyed races, even whole worlds, and sometimes he enjoyed doing it. He’s capable of so much violence and he’s offering to show it to Red if he’ll jump into him. The Red suspects it’s a trick, but the Doctor points out that they’re still linked, so he can’t harm him without harming himself. But the Red had also discovered what Mel is doing…

…and in the outside world, the Red jumps into Nuane, who then approaches Mel at the computer console. Thousands of lives depend on Mel finishing her work, but there’s still one command that keeps locking her out. As Nuane attacks Mel, Draun grabs his sister and pulls her off. Yulquen asks for Draun’s knife and says she has no qualms about using it on Nuane. Draun tries to stop her, but in the struggling Yulquen ends up plunging the knife into him instead!

Inside slow time, the Doctor senses the Red’s confusion as Draun dies. He urges the killer to let Nuane go and take him instead - but when it does so, the Doctor welcomes him to his trap! The Doctor has bottled his violence up for so long and now he can let it all out. He’s a killer too and it’s time to kill the Red. The Red says it has returned from the dark space of the ether and has now synchronised with the Doctor, so he can’t hurt it. It speaks to him in the voice of Celia and tells him that she liked the killer inside her as it enabled her to hurt lots of people, but the Doctor knows that in the end Celia didn’t want that. She paid the price for her actions and now the killer wants to feed instead on the Doctor’s violence. But the Time Lord also has special abilities and he’s able to mentally crumble to crystalline nervous system that Slow created, while keeping the Red trapped inside his chip. He pushes the killer back inside the machine…

…and then the Doctor ’fast-forwards’ back to normal time. Unfortunately Mel still hasn’t completed her work and Whitenoise is continuing with its mission to kill all the residents by burning out their chips. Worse, his own chip is still active - which means the Red can escape through it, and it’s only a few seconds behind him. Mel explains that she was stumped by a command override on the computer, and when the Doctor takes over even he is unable to shut Whitenoise down. As a last resort, he and Mel have no choice but to simply pull out all the computer’s wires. The system itself is still operating, but the chips have been deactivated. Mel has discovered that Blue had already installed a self-destruct algorithm for just such an eventuality. The only question remaining is who wants to be the person to press the self-destruct button…?

To Yulquen’s horror, Nuane volunteers without a second‘s pause. Yulquen is terrified at the prospect of having to live outside the Needle, but the Doctor says they have no choice. The Needle itself is going to self-destruct, so they need to find as many survivors as they can and evacuate. In its dying moments, Whitenoise tells them some of the residents have escaped already, but the majority are still inside. Nuane believes people like Yulquen deserve to die in the building and the Doctor is about to argue with her morality when the building starts to collapse. He estimates they have about sixty seconds to reach the TARDIS…