With the help of his old friend, Detective Inspector Bob Lines, the Doctor has successfully prevented the Master and his Usurian cohorts from destabilising the world economy. Now, he must remove all trace of alien interference from the world's banking systems, but he requires assistance to do so, as the computer languages of the year 1989 are too primitive for him to understand. While Lines searches for an expert, the Doctor sets off to explore the city of Brighton -- only to spot his future companion Melanie Bush walking down the street with a friend. He has been trying to avoid meeting her, knowing that if she joins him on his travels he will have taken one step further towards his destiny as the Valeyard -- but he now realizes that Lines is likely to enlist her help. While considering his situation at a fast food restaurant, Nessie Burger, the Doctor once again encounters Mel's friend, an American exchange student named Trey Korte. Trey is impressed when he sees the Doctor hand over his free plastic toy to a little girl who wanted it to complete her set. Somehow sensing that this odd man is a genuinely good person, Trey follows the Doctor out of the restaurant to learn more about him, only to collapse in pain upon seeing the TARDIS. The Doctor realizes that Trey's latent psychic abilities have been jump-started by his exposure to the TARDIS, and hires a taxi to take the recovering young man home -- realizing too late that this is the home of Melanie Bush. He is also unaware that Trey's psychic spasm has been noted by two employees of the company SenéNet, who inform their managing director that they have found a suitable esper for the next stage of their plan...
Mel is working at Brighton Information Technologies for the summer, gaining experience before accepting a position at Ashley Chapel Logistics. When her boss' nephew Luke fails to return from a business lunch with executives from SenéNet, Mel becomes concerned and phones her father to ask if he's heard anything about the company -- but she hears a click on the line and realizes that her conversation is being monitored. She does not ask any further questions, but her interest has been noted by SenéNet's managing director -- Martyn Townsend, the former director of the Vault, Department C19's storehouse of alien technology. Meanwhile, he attends a meeting with a Japanese businessman whose company is manufacturing a 64-bit games console called the Maxx for SenéNet. Futayomoto has refused to install the programmes supplied by Townsend until the purpose of the code is explained to him; Townsend therefore uses alien technology to erase Futayomoto's mind and reprogramme him with new instructions, and replaces his blood with a polymer compound which will carry commands through his body more efficiently. Townsend's assistant Jones, who has found that the thrill of killing has faded with time, releases Futayomoto's aides into the forest to be hunted by the Stalker, a hound augmented with the primordial Stahlman's gas.
The Doctor introduces himself to Mel and her parents, who are frankly sceptical about is claim to come from another world but are nevertheless grateful for his helping Trey. Despite his desire to avoid the future that Mel represents, the Doctor can't bring himself to snub her, especially when he learns that Bob Lines has indeed called her in as a consultant. He advises her to return to work at BITS until they're ready for her at the police station, but Townsend has had Mel's boss killed, and when she arrives at work she finds the oddly distant Luke in charge of the company. Luke claims that he has dropped all of BITS' old clients; from now on they will only be serving SenéNet. Unnerved by his odd behaviour and the clammy texture of his grasp when they shake hands, Mel quits her job, convinced that there is something odd going on. Meanwhile, the Irish Twins Ciara and Cellian -- associates of Townsend who have been augmented by Nestene technology to become more efficient killers -- kidnap both Trey and Mel's mother Christine from their home and take them to SenéNet. Elsewhere on the SenéNet grounds, a bitter man with a half-melted face brings food to his prisoner -- Alistair Gordon Lethbridge-Stewart, who is uncertain why his jailer seems to have a personal grudge against him.
While reading the local newspaper the Doctor finds a coded message from Sir John Sudbury of C19 which indicates that Lethbridge-Stewart is missing. The Doctor calls Sudbury for more information, and Sudbury explains that Lethbridge-Stewart vanished three weeks ago after being called out of retirement to investigate the suspiciously advanced technology being marketed by SenéNet. Futayomoto's aides are then found in the woods, one of them mauled to death by an unidentified animal, and the other hiding up a tree. While Lines seeks an interpreter to question the terrified businessman, Mel finishes her work with the computer systems. When she learns that the Doctor intends to investigate SenéNet, she insists upon helping despite his efforts to dissuade her, hoping to learn what has happened to her friends at work. Having learned from the paper that SenéNet is sponsoring the toy giveaway at Nessie Burger, the Doctor purchases a number of the toys to investigate further, and discovers that they are all cold and clammy to the touch despite having been packaged up with hot food. Mel realizes that the odd texture of the toys is similar to the feel of Luke Aspinall's hand that morning...
Lethbridge-Stewart finally provokes his jailer into revealing that he is a former UNIT soldier, wounded and left for dead after the Axon invasion; when the C19 cleanup crew found him, he gladly agreed to work for Townsend, blaming the Brigadier for abandoning him in the wreck of the Nuton power facility instead of searching for survivors. Lethbridge-Stewart, however, knows the name of every man who died under his command, and like every commander is haunted by his failures; he knows Erskine well, and he points out that if Townsend had wanted to, he could easily have used his pilfered alien technology to heal Erskine's burned face. Townsend has no intention of using his hoard to improve the quality of life on Earth, and has deliberately left Erskine scarred so he will continue to hate those who reduced him to this. Erskine realizes that Lethbridge-Stewart is right, and is forced to reconsider his loyalties. Townsend, however, realizes that Erskine is having doubts -- as are Ciara and Cellian, who are finally coming to understand just how much humanity they gave up when they were converted into Auton hybrids. Even Jones is growing less efficient, as proven by the survival of one of Futayomoto's aides. Townsend too is dying, as the cybernetic body he acquired while working for Tobias Vaughn is failing and the parts he needs are not available on twentieth-century Earth. However, his new allies have provided him with a new body, and all he needs to transfer his mind into it is a spark of psychic energy -- to be supplied by Trey Korte. Once this is done, he will use the alien technology in his possession to conquer the world.
The Doctor and Mel search for clues in the woods outside SenéNet, but they are spotted and Jones kidnaps Mel while the Doctor is distracted. The Doctor returns to Pease Pottage to collect Trey, hoping he can help, only to find that Trey has also been kidnapped. When he tries to report the situation to Lines he finds that a SenéNet assassin -- Cellian -- has killed the surviving Japanese man while posing as an interpreter. News then breaks of a terrible tragedy in the city, as nine children have suffocated to death on their Nessie Burger toys -- but the Doctor learns that they were all winners of SenéNet's promotion and had been playing with their Maxx consoles at the time of their deaths, and deduces that this was in fact a test run for SenéNet's true agenda. Further investigation confirms that SenéNet has recently introduced a new form of polymer-based coaxial cables to Brighton, through a company director who retired immediately after introducing the new technology and was subsequently killed in a car crash. The Doctor finally realizes that SenéNet is an anagram, and concludes that the Nestenes are once again attempting to conquer the Earth, by setting up a network of polymer cables which will transfer their consciousness into every home on the planet.
Mel awakens in a hospital on SenéNet grounds, where she finds the unconscious Christine and Trey and is confronted by the sinister Dr Ingrid Krafchin, who is in charge of converting humans into Nestene replicas. Mel is then placed in a cell with Lethbridge-Stewart, who has realized that Townsend is keeping him alive in order to break his spirit and interrogate him about classified UNIT operations. Erskine helps them to escape and kills Jones when he discovers them, but security officer Lawson finds the body and releases the Stalker. Mel leads it away into the woods, while Lawson captures Erskine and Lethbridge-Stewart and brings them before Townsend. Meanwhile, Ciara and Cellian pursue Mel into the woods, but the Stalker attacks them and seriously wounds Cellian before Ciara can kill it. Seeing her brother near death and realizing that she feels nothing for him, Ciara finally realizes how much she has lost, and tells Mel to warn the Doctor that Krafchin is the key to the whole operation. Ciara then collects Townsend's agents, bystanders who had been literally reprogrammed to serve SenéNet, and takes them and her brother away, hoping to atone for her crimes by finding some way to restore the agents' minds.
The Doctor decides to confront SenéNet's managing director in person, and takes Alan Bush's mobile phone in order to inform him should he find Christine and Mel. Upon arriving at SenéNet's building the Doctor is brought before Townsend, whom he soon recognizes. Townsend takes him to the cellars of the building, where he stores his pilfered alien technology -- and the new plastic body created for him by two dormant Nestene energy units. Townsend believes that the energy units serve him alone, but the Doctor realizes that they are not damaged at all -- and when Krafchin is revealed to be an Auton Replica animated by an active energy unit, he realizes that it is the Nestenes who are really in charge here. Trey's powers will be used not to transfer Townsend's mind into his new body, but to reunite these isolated energy units with the greater Nestene Consciousness -- and when the Maxx consoles and their polymer control cables are distributed across the world, it will not be Townsend who controls them, but the Nestene Consciousness. Townsend's desire for power and immortality blinds him to the truth, however, and he orders two Autons to guard the Doctor while he connects Trey to the machinery. The Doctor, realizing that Alan's mobile phone is still in his pocket, surreptitiously tries to rewire it by touch alone to transmit a jamming signal.
Despite the Doctor's warning not to interfere, Alan finally reports the kidnappings to Bob Lines, who leads a CID team to SenéNet. There, they are reunited with Mel, and Lawson is killed trying to prevent them from storming the building. The Doctor manages to transmit the jamming signal and thus saves Trey from being absorbed into the Nestene Consciousness. Erskine takes advantage of the distraction to attack Townsend, but is killed, and an Auton then attempt to shoot the fleeing Doctor -- only to blast a hole through the wall and the pipes supplying water to the ornamental fountain in the grounds. As the cellar floods, Townsend scrambles towards his new body while the others evacuate -- and the flooding water hits exposed electrical equipment, causing a chain reaction of fires and explosions which kill Townsend and destroy his collection of alien technology. As the survivors deal with the aftermath, the Doctor bids a fond farewell to his old friend Lethbridge-Stewart and prepares to depart alone; but Trey, reading Mel's mind, realizes what she intends to do and tells her where she can find the TARDIS. Mel thus reaches it first, causes a distraction when the Doctor opens the door and stows away on board. The Doctor bows to the inevitable and allows her to accompany him on his continuing tour of the Universe.
Source: Cameron Dixon