It is just after 8:00 a.m. on 21 October 2021 at St Gart’s Brookside, a London hospital belonging to the Euro Combine Health Administration. Dr Stephen Farrer is attending Subject One, a participant in the “Recarnative Program”. Subject One appears happy with his current condition, and the fact that he can feel any emotion at all suggests that the operation has been a qualified success. The patient is fascinated by the new sensations he’s experiencing, but Farrer tells him that the novelty will wear off as he moves on to more complex emotions and experiences. Subject One does not seem to be looking forward to that.

The hospital’s AI, System, then informs Farrer that Executive Security Officer David Garnier needs to speak with him, and Farrer leaves Subject One to experience the warmth of sunlight on his flexing, muscular hand. Unfortunately, Garnier is here with bad news: Subject Four has rejected a critical graft, and they’ve run out of tissue matches in the C-Programme reserve banks. Farrer manages to restrain himself from taking out his frustration on Garnier, knowing that Garnier is doing his best to juggle conflicting priorities: keeping the Subjects alive, meeting the timetable set by their superiors in the Hague, and keeping a lid on C-Programme’s activities. Nevertheless, Subject Four will die unless Farrer operates, and he thus orders Garnier to find a matching tissue type -- as quickly and discreetly as possible.

Meanwhile, staff nurse Thomas Hector Scofield, known to his friends as Hex, arrives at St Gart’s to start his working day. It’s also his birthday, and Dr Mark Matthias, a junior attending A&E doctor, has arranged a blow-out at the pub that night -- and, much to Hex’s embarrassment, Mark has invited practically every single female staff member Hex has ever shown an interest in. When Hex complains about the broken coffee machine in the atrium, Mark asks a passing janitor to fix it, but the janitor, a man with a Scottish accent, seems to have other things on his mind. The day then kicks into high gear with the arrival of a bike courier who was involved in a traffic accident. His skull is fractured, he’s already suffered cardiac arrest -- and, as Hex cleans up the blood and preps the body, he recognises the injured man as his friend and former flatmate, Damien Boyd. It’s the first time Hex has seen one of his friends on the operating table, and, realising that Hex is having trouble focussing on his work, Mark kindly invites him to step outside for a moment. As Mark consoles the shaken Hex, Dr Farrer arrives, apparently having been paged to help. Farrer reviews Boyd’s chart and agrees to operate on him in nanosurgery, and Hex, knowing Farrer’s reputation, is somewhat relieved.

Later, while buying lunch in the atrium cafe, Hex meets a new hospital employee, a young woman from Human Resources who introduces herself as “just McShane.” Mark has also invited McShane to Hex’s birthday party, and after meeting him personally, she decides to accept the invitation, realising that the young man needs cheering up. McShane then returns to work, as does Hex, but Hex first takes the lift up to floor 31 to check on Damien’s condition. Hex’s log tags don’t clear him for access to this floor, and when he arrives, Garnier tries to kick him out. Hex spots Farrer and asks after Damien, and is stunned when Farrer coldly informs him that Damien died on the operating table. When Hex reveals that Damien was his friend, Farrer becomes more sympathetic, and despite Garnier’s objections, offers to let Hex see Damien’s body, which will remain in the morgue until claimed by his next of kin. Hex turns down the offer and retreats to the lift, shocked by his friend’s death.

That night, Hex attends his birthday party, but he’s in no mood to celebrate and leaves early. Outside, he bumps into McShane, who’s just arriving. She soon deduces what’s happened, and insists upon talking with him and calming him down before he drives off in his scooter. She is oddly interested when Hex reveals that Dr Farrer failed to save Boyd’s life, but Hex can’t tell her much about Farrer, since the well-funded research and nanosurgery divisions don’t tend to mix with the other departments. McShane then asks Hex if he’s ever heard of anything called C-Programme, which he hasn’t -- but as they speak, a device in McShane’s pocket starts to beep. She claims it’s a cell phone, but in fact, it’s warning her that their conversation is being monitored. A man named Polk is sitting in a Mercedes at the end of the lane, and he now decides to take action...

McShane bids Hex a happy birthday and starts to leave, but the Mercedes drives up and nearly runs them down -- and as the appalled Hex watches, the Mercedes stops, reverses, and tries to hit them again. Realising that the man in the car is deliberately trying to kill them, Hex insists that McShane board his scooter, and he drives her to safety, evading the Mercedes by driving onto a pedestrian walkway. The man from the Mercedes emerges and chases them down the walkway, and Hex is stunned by the figure’s inhuman size and incredible speed. Nevertheless, he manages to outpace the running figure, and McShane claims that Hex must have misinterpreted how tall and fast he was in the heat of the moment. Hex isn’t convinced, but agrees to give McShane a lift back to her lodgings in Shoreditch.

The stunned Hex tries to convince himself that this is a gag put on by Mark and his friends, and must sit down to catch his breath when it becomes clear that it’s nothing of the sort. McShane and the Doctor claim to be private investigators, and the Doctor takes McShane to task for getting an innocent man involved in their work; however, McShane insists that Hex involved himself, and suggests that he might be able to help them. The Doctor isn’t so sure, as Hex is having trouble just coping with the TARDIS; however, Hex is willing to listen to what they have to say on condition that he be allowed to freak out a little about it. The Doctor thus explains that he and McShane are investigating the experiments being conducted on the 31st floor of St Gart’s; they have reason to believe that the European government has acquired technology of extra-terrestrial origins and is attempting to reverse-engineer it to gain an advantage in the space race. The Doctor and McShane are here to put a stop to it, and after weeks of effort, the Doctor believes that he’s finally managed to convince System that McShane has the authority to get into the 31st floor. Also, for the record, the TARDIS looks like a police box, not a public toilet. Hex is shaken by these revelations, except possibly the last one, but agrees to help investigate.

Farrer has successfully stabilised Subject Four’s condition, but Garnier then reports a disturbing incident to him. It seems that a certain Dorothy McShane from Human Resources has fabricated her employment record, and, earlier, she was spotted discussing C-Programme with the same staff nurse who spoke to Farrer about Damien Boyd. Farrer had assigned Polk to keep her under observation as a test of Polk’s abilities, but it seems that Polk went beyond the call of duty, alerting McShane to the fact that they’re on to her. Fearing that the programme has been infiltrated by foreign spies, Farrer authorises Garnier to use all of the emergency powers at his disposal to keep a lid on this.

The next morning, Farrer addresses Subject One, who is now able to stand without difficulty; however, he must still remain connected to life support systems to survive. Subject One expresses an interest in the project’s progress, and Farrer assures him that the other subjects of the Recarnative procedure are doing very well. He also introduces Subject One to Polk, the first active prototype from C-Programme’s other division. Garnier escorts Polk through the room, and Subject One notes that Garnier seems disturbed by the sight of him, as if Subject One’s appearance is particularly revolting. Farrer reluctantly admits that Subject One is displaying some tissue swelling and visible suturing, but assures him that this is only temporary. However, Subject One was merely curious because he considers Polk to be a far more terrifying creature.

It’s just after 8:00 a.m. again, and this time, Hex accompanies the Doctor and McShane to the hospital. The Doctor gives Hex one last chance to back out, but Hex now considers himself fully involved. The Doctor thus hands him and McShane a pair of earphones, micro-voice transceivers which will enable all three to stay in contact. McShane and Hex enter the atrium through the front doors, using false log-tags to get inside without alerting System to their true identities; meanwhile, the Doctor nips around the side entrance and types in a false identification code granting him access to facilities normally available only to hospital ancillary staff. System thus allows the Doctor to open a maintenance locker and retrieve a toolcart and set of janitor’s overalls, even though it knows it should be activating security alarms instead.

While McShane and Hex wait for the Doctor to get into position, McShane gives Hex some advice on how to deal with the bizarre situation he now finds himself in. However, she refuses to tell him why the Doctor sometimes calls her “Ace”. Mark then flags Hex down, wanting to know where he disappeared to last night, but when he realises that Hex and McShane are together -- and apparently have been since Hex left the party -- he leaps to a rather personal wrong conclusion. McShane plays along and claims to need Hex’s help to go over paperwork, and Mark, winking ostentatiously, disappears in search of aspirin for his hangover. Hex is relieved by this close call, but McShane informs him in no uncertain terms that Mark was hungover and an idiot, and that the people they’re up against are much more dangerous and focussed. Hex allows this to sink in, but nevertheless insists upon helping her.

On the ninth floor, the Doctor orders System to open maintenance hatch 915, thus gaining access to its central data core. Though distressed by what the Doctor is doing, System finds that he is apparently fully authorised to carry out these procedures. Using Gallifreyan technology up to and including his sonic screwdriver, the Doctor connects a portable data terminal to System’s stacks, and grants both McShane and Hex access to C-Programme’s restricted sectors. However, when they try to take the lift to floor 31, System denies them access -- and the Doctor discovers that, in the few minutes since he rewrote System’s commands, they’ve been rewritten yet again by “username silver”. Apparently, new security procedures have been implemented since last night. McShane and Hex retreat to the atrium while the Doctor tries to find out what went wrong, and Hex then comes up with an alternative plan: Mark has access to the morgue on level 30, and if they can convince him to take them there, they might be able to find another way into the floor above. While Hex and McShane set off to speak to Mark, the Doctor accesses Hex’s personal information in System, planning to adjust his security clearance. But amongst the details such as Hex’s date of birth and place of education, the Doctor finds something rather intriguing.

Meanwhile, in C-Programme, Polk reports to Garnier that someone has made an unauthorised attempt to enter the 31st floor. The CCTV camera was scrambled at the junction in question, implying that the spies have access to System. In response to this serious breach of security, Garnier orders Polk to activate all 20 of the current C-Programme prototypes...

Hex manages to escape, but the Cybermen capture Mark and McShane, and the Doctor loses contact with McShane. Nevertheless, he calms down the panicking Hex, insisting that he did the right thing by fleeing. Security guards are out in force, and the Doctor directs Hex to walk calmly back to the atrium and out of the hospital while the Doctor disconnects his data terminal, planning to join him outside. Garnier and two security guards grab Hex steps away from the entrance, but the Doctor arrives and sets off a harmless but very loud explosion using chemicals from his cleaning supplies. In the confusion, he and Hex get out of the hospital, flag down a taxi and retreat to Shoreditch. On the way, the Doctor gives Hex a run-down of the Cybermen’s history, explaining how the people of Mondas, with the best of intentions, transformed themselves into implacable, conscienceless killing machines. It’s a tragic story which the Doctor is determined to prevent from unfolding again on Earth, but now that the hospital has increased its security and McShane is in immediate danger, that means he’ll have to forego the subtle approach and take a more direct route to the 31st floor.

The taxi driver drops off the Doctor and Hex back at the car park in Totters’ Lane, and they return to the TARDIS. In broad daylight the interior is even more unbelievable, but Hex manages to contain himself, after a fashion, and accepts the Doctor’s explanation that this weird machine can travel anywhere in time and space. However, short, specific jumps are extremely difficult to manage, and if the Doctor misses the target slightly, he’ll materialise either inside a wall or outside the hospital, 31 floors up. Nevertheless, he now has little choice but to try.

Back in C-Programme, Polk marches McShane and the increasingly bewildered and terrified Mark through a laboratory in which human bodies are being harvested for organs and tissue. Garnier then interrogates them, revealing that the powers granted to him by the Euro Combine enable him to do whatever he wants to them without question. Mark offers to sign a non-disclosure waiver, and Garnier dismisses him as an unimportant buffoon who’s stumbled into something beyond his understanding. McShane is a different matter, but she refuses to tell Garnier anything useful; however, she does catch him off guard by referring to the Cybermen by name. Now convinced that she’s a dangerous foreign spy, Garnier leaves her to ponder just what use C-Programme may put her to if she refuses to co-operate. But as Garnier retreats, McShane warns him that, whatever he may think, it’s really the Cybermen who are in charge here.

Subject One has rejected another graft, and Farrer must operate to remove the dead tissue. Subject One insists upon remaining conscious during the operation, claiming that he wishes to experience every new sensation, including pain. This is the third time his new body has rejected a graft, however, and he’s becoming concerned. Farrer assures Subject One that all will be well, but becomes disturbed when Subject One compliments Farrer on his own strong, gifted hands... and squeezes them just a bit too hard. Garnier then arrives to report that McShane has been captured, and Farrer privately admits that his optimism is just a show for Subject One’s benefit. Every one of the subjects has suffered massive graft rejections, and Farrer is beginning to doubt whether he can keep them alive. Garnier wonders whether it’s even worth the effort, but Farrer insists upon doing all he can to keep his patients alive. This means that the organ banks must remain fully stocked... and Garnier thus collects his prisoners from storage, deciding not to bother interrogating McShane any further. She can serve a much more useful purpose -- at least, bits of her can...

The TARDIS materialises successfully on the 31st floor of St Gart’s, and the Doctor and Hex emerge to find themselves in a facility more like a military installation than a hospital. The block is completely sealed off, and the exterior windows have been blacked out. The Doctor and Hex hide to avoid a patrolling Cyberman, which is of a cruder build than the Doctor had expected, and then explore their surroundings. As the Doctor had feared, the Cybermen seem to have set up a mass-production factory to manufacture spare parts for an army of their kind -- yet, oddly, the parts are being tailored to specific human beings. Normally, the Cybernisation process tailors the human form to the cybernetic parts, but this time it’s being done the other way around. On a nearby data terminal, the Doctor finds detailed information on the recent converts -- Craig S. Vincent, John Parsons, Christopher C. Polk, Jonathan S. Small, and Andrew M. Lanning, amongst others. Every one of them is an astronaut or science officer attached to the space programme, and every one of them signed an affidavit confirming that they had volunteered for the process. The C-Programme is giving the European government a boost in the space race by creating cybernetic astronauts capable of surviving in the depths of space with little or no life support.

Further on, the Doctor and Hex stumble across an organ storage facility containing bodies harvested from the morgue; these are the brain-dead, their bodies kept technically alive to supply tissue and organs to C-Programme. It occurs to the Doctor to wonder why the project needs organic spare parts if they’re supposed to be converting human beings into Cybermen. As he ponders this, Hex stumbles across the body of his friend, Damien Boyd. The Doctor urges the stricken Hex to keep himself together, but at that moment, another of the prototype Cyber-humans discovers them, and they are forced to flee. The Doctor draws the Cybermen away from Hex, who stumbles into an automated nano-surgical lab. He hides when Farrer enters, and watches as Farrer calls up displays on Subjects Two and Seven, the latest to have suffered serious tissue rejection. Before Farrer can order System to search for suitable matches in the organ banks, Garnier arrives with Mark and McShane -- and orders Farrer to harvest the parts he needs from them. The horrified Farrer refuses; harvesting tissue from the dead is one thing, but murder is a step too far. However, Garnier points out that their deal with the Cybermen requires them to do all they can to keep the seven subjects alive, and when Farrer continues to protest, Garnier orders Cyber-human Parsons to remain in the lab and ensure that Farrer carries out his orders. Garnier leaves, and Parsons straps down the protesting Mark and McShane and orders Farrer to begin his work. When Farrer hesitates, Parsons uses force to make him start the auto-surgeons.

The Doctor loses his pursuer near an interesting locked door. He breaks the combination and enters to find himself facing Subject One, and when he questions the figure, he learns that Subject One is a former Cyber-Leader. Just as humans are converting themselves into Cybermen here, the Cybermen are apparently converting themselves back into organic beings, though, from Subject One’s appearance, it seems the process has some problems to iron out. Subject One eventually realises that the Doctor is not authorised to be in this area, and Garnier then arrives with Polk, sees the Doctor, and orders Polk to kill him.

Hex emerges from hiding and tries to shut down the auto-surgeons, but Parsons hauls him back and begins to throttle him. To save Hex’s life, Farrer attacks Parsons with a bone saw, cutting right through the Cyber-human’s neck. Shocked by what he’s done, Farrer pulls himself together and shuts down the auto-surgeons moments before they begin to cut Mark and McShane apart. Once free, Mark punches Farrer in the nose, but Hex and McShane stop him from doing any further damage. However, alarms begin to sound off, and Farrer reveals that the Cyber-humans are all networked -- and the others will now know what’s happened to Parsons. The four of them flee, hoping to use Farrer’s log-tags to get to safety.

Subject One prevents Polk from killing the Doctor; though he is no longer directly connected to the Cybermen’s data archives, he remembers the Doctor nevertheless, as do all Cybermen. Garnier tries to assert his authority and have the Doctor killed, but Subject One calls on System to scan the Doctor’s physiognomy, thus proving that he is not a human being, but an alien Time Lord with the technical knowledge and skills to complete the Recarnative programme. When this sinks in, Garnier tries to assert his authority to draft the Doctor into C-Programme, but the Doctor laughs in his face; he will not help to transform the people of Earth into Cybermen, particularly not to help a bureaucrat like Garnier further his petty ambitions. Garnier threatens to set Polk on him, but the Doctor points out that Polk seems distracted. Polk informs Garnier that Parsons has been destroyed, and though Garnier insists that the others can take care of it, Polk demonstrates the single-mindedness of a Cybermen and insists that his top priority is to protect C-Programme. Frustrated, Garnier gives Polk the authorisation codes to open the weapons locker and sends him on his way. The Doctor fears that Garnier has just made a catastrophic error of judgement...

Nevertheless, the Doctor agrees to listen to what Subject One has to say. Subject One thus explains that his expeditionary force crash-landed in the Pyrenees, where their ship was found by a European Council team. The damaged Cybermen, cut off from their own kind, struck a deal with the Euro Council -- and though the Doctor understands that the Europeans are now using Cyber-technology in their space programme, he’s startled by what the Cybermen asked for in return. The people of Mondas transformed themselves into Cybermen to survive on a cold, dead world in the depths of space -- but Earth is a living, vital planet, and here, the former Cybermen have a chance to live ordinary organic lives once more. The Doctor, initially sceptical, is astonished to find himself believing the former Cyber-Leader’s claim that he and the other Subjects now wish to rediscover the benefits of an organic life rather than an existence as cold, calculating machines.

Before the Doctor can decide whether Subject One is telling the truth, System informs Garnier that Subjects Two and Five are suffering from serious graft rejection and that Farrer is not answering his pages. Garnier marches the Doctor off to the surgery to put his talents to use, and Subject One accompanies them. Unlike Subject One, the other six former Cybermen are currently suspended in bio-support tanks, unable to survive outside their confines, and dying slowly as their new, organic bodies reject the tissue grafts which Farrer has provided for them. Though moved by the Cybermen’s claim to seek redemption, the Doctor isn’t sure whether he can save their lives -- and in any case, he refuses even to try unless Garnier agrees to shut down C-Programme and stop manufacturing Cyber-humans.

Meanwhile, the Cyber-humans are dealing with the death of Parsons in an unfortunately logical manner. Since Parsons was killed by a human, humans must therefore pose a threat to the programme, and since the programme must be protected, these threats must be eliminated. Polk thus uses Garnier’s authorisation codes to open up the weapons locker, and the Cyber-humans fan out through C-Programme, gunning down every unconverted human they encounter. Farrer, Mark, McShane and Hex watch from hiding, horrified but incapable of intervening. Since Garnier outranks Farrer in security matters, Farrer cannot order the Cyber-humans to stop -- and McShane fears that it won’t be confined to the 31st floor, or even to St Gart’s. However, Farrer reveals that he has a way to stop the slaughter; he’d feared the consequences of empowering the prototypes without including a failsafe, and he thus installed a master cut-out which he can arm and trigger if he can get to his office. However, this will mean running a gauntlet of armed and dangerous Cyber-humans.

Garnier refuses to do as the Doctor demands, insisting that the Cyber-humans have been created for the good of mankind and that he is in full control of them. Subject One points out that his comrades, and even himself, are suffering from catastrophic organ failure, and begs the Doctor not to hold their lives to ransom for his principles. But the Doctor stands firm -- and when Polk arrives, even Garnier can’t ignore the sound of screams and gunfire he hears through the open door. Polk reveals what the Cyber-humans are doing, and the appalled Garnier orders him to stand down -- but Polk refuses. Before Garnier realises what’s happening, Polk shoots him dead, eliminating another human threat to the programme. The Doctor expects to be next, but instead, Polk orders him to obey the commands of the Cyber-Leader, and the horrified Doctor realises that Subject One has indeed rediscovered the benefits of an organic mind and body -- including the ability to lie convincingly. The former Cyber-Leader has been in control of the Cyber-humans all along, and the Euro Combine has unwittingly helped the Cybermen to set up a processing factory in the heart of London with a cadre of free-thinking Cyber-Leaders at its head. The invasion has begun, and Earth will be dominated by the Cybermen within six weeks. Subject One now orders the Doctor to complete the Recarnative programme and restore him and his comrades to full health, but the Doctor refuses, and Polk therefore prepares to shoot him.

McShane and the others very nearly make it to Farrer’s office before the Cyber-humans spot them. Farrer is all but torn apart by the ensuing hail of bullets, but Hex and Mark manage to carry him into the office and lock the door. Mark is also shot in the arm, and he begins to go into shock; however, Hex bullies him into pulling himself together and helping to stabilise Farrer’s condition. Meanwhile, McShane tries to log onto Farrer’s data terminal, but just as she discovers that she needs a password to shut down the Cyber-humans, Mark passes out from shock and blood loss. As the Cyber-humans batter down the door of the office, Hex struggles to keep Farrer conscious just long enough to reveal the password: “harvest”. McShane types it in as the Cyber-humans tear the door off its hinges...

Subject One has ordered Polk to kill the unco-operative Doctor, but instead, the termination protocol is activated and Polk drops dead. Subject One screams in rage when System confirms that all Cyber-humans have shut down, and the Doctor simply walks away, leaving Subject One to collapse and flatline as his internal organs finally fail him. The last new organic sensation Subject One experiences is fear.