The Doctor and Melanie arrive in a dingy tower block, somewhere in post 21st-century Earth. They were expecting their destination, Paradise Towers, to be more welcoming on the basis of the architectural awards it has won. The building is divided between roaming gangs of young girls called Kangs, grouped in colour theme, and the Doctor and Mel encounter the Red Kangs. They have just discovered the death of the last Yellow Kang and are plotting how to attack the Blue Kangs. Elsewhere in the Towers, one of the Caretakers - who act as 'Judge Dredd' style policemen – is hunted down and killed by a robotic cleaner, which seems to appeal to the sadistic Chief Caretaker when he overhears the death.
The Chief then sends a squad of Caretakers to arrest the Red Kangs and in the ensuing confusion the Doctor is split from Mel and captured by the Caretakers. Mel meanwhile heads off to one of the still occupied apartments in which two elderly ladies ('rezzies') live. Tilda and Tabby explain that all the able bodied men left the Towers to fight a war letting the young run riot (the Kangs) while the old stay in their chambers. The only other character still loose in the Towers is Pex, a would-be hero, who whisks Mel away to try and find the fabled swimming pool of the Towers.
At the Caretaker control centre the Doctor is delivered to the Chief Caretaker who greets him as the Great Architect, designer of Paradise Towers, and then promptly calls for him to be killed.
The Doctor challenges the bureaucracy and complex rules of the Caretakers, using their rule-bound nature to make his escape. This appals the Chief Caretaker, who is obsessed with visiting and feeding a hidden tank in the basement of the Towers. Mel and Pex meanwhile have headed to the top of the building, and are there captured by a party of Blue Kangs. Before the pair are freed the Kangs delight in telling Mel that Pex survived by fleeing from the war.
The Doctor finds the Great Architect is named Kroagnon – a name which seems strangely familiar – and is reunited with the Red Kangs. They explain that many members and Caretakers too have been disappearing in ever greater numbers. While he is being interrogated it becomes clear the Caretakers have tracked him down to the Red Kang headquarters and start to break down the door to their headquarters. Elsewhere Mel has visited Tilda and Tabby again and soon finds herself under threat when it emerges they are cannibals and plan to eat her.
The Doctor succeeds in holding off the Caretakers long enough for the Kangs to flee. Meanwhile Tabby and Tilda are delayed in their eating of Mel when they are disturbed by a noise in the waste disposal. It turns out to be a metal claw, which first drags Tabby to her death in the disposal system, and then Tilda after Pex arrives and finds heroism when he somehow succeeds in saving Mel from her clutches. Mel and Pex find a map of the Towers and decide to venture to the roof, where the luxury swimming pool is located. En route they are menaced by a robotic Cleaner.
The Doctor has meanwhile been taken to the Caretakers HQ again, where he realises that the Chief Caretaker has been allowing the Cleaners to kill people in the Towers, but that the killing has now got out of hand and the Chief Caretaker is no longer in control. This fuels the Chief’s paranoia and fear, and the situation gets worse when the report arrives of the death of the two rezzies in the waste disposal. The intelligence the Chief keeps in the basement is demanding more sustenance and making its own hunting arrangements. When the Chief heads off to investigate the deaths of Tabby and Tilda, the Red Kangs attack the HQ and rescue the Doctor. He returns with them to their base, taking with him the Illustrated Prospectus for the Tower, which they all watch. It reminds the Doctor that Kroagnon, the Great Architect of Paradise Towers, also made Miracle City, a cutting edge development which killed its occupants. It seems Kroagnon had an aversion to people actually populating his buildings. The Blue Kangs arrive suddenly, overpowering the Red ones, but it soon becomes clear their game is over and they must now work together.
When Mel and Pex finally find the swimming pool, Mel takes a dip inside only to be attacked by a robotic killer crab.
The Red Kangs know of the monstrosity in the basement, and guess it must be linked to the terror in the Towers. The Doctor heads off to investigate and there finds the Chief has been herded by the Cleaners toward the mysterious intelligence, which turns out to be Kroagnon himself. The Doctor is soon spotted by the Cleaners too, and the robots start to attack.
The Kangs rescue the Doctor in the nick of time while on the roof Pex fails to rescue Mel, who has to destroy the crab herself. When the Doctor and the Kangs arrive, the latter taunt Pex for his cowardice. The Doctor explains that Kroagnon, the designer of Paradise Towers, felt human beings would ruin his creation and so placed multiple deathtraps throughout the Towers before he was killed and trapped in the machine in the basement. The remaining rezzies(who, unlike Tabby and Tilda are not cannibals), led by a woman named Maddy, join them all at the swimming pool and pledge to work together with the Kangs to defeat the menace in the building. Pex pledges to help too. The Deputy Chief Caretaker and the surviving Caretakers, who have become convinced of the peril in the basement too, soon join them.
The Chief Caretaker has now been killed and his corpse animated by the artificial intelligence of Kroagnon. He now intends to use the Cleaners to kill everyone in the Towers and repair the damage the “filthy human parasites” have caused. However, the combined human forces are now fighting back against the machines. The Doctor and Pex also devise a ruse to lure the Chief into a booby trapped room and thereby destroy Kroagnon, but when the plan becomes derailed Pex sacrifices himself to drag the Chief into the trap. They are both killed, but the terror is over.
After a period of reflection and Pex’s funeral, the Doctor and Mel leave Paradise Towers, trusting the remaining Kangs, Rezzies, and Caretakers to build a better society. As the TARDIS dematerialises, a new piece of Kang graffiti is revealed - "Pex Lives".
Doctor Sylvester McCoy (Seventh Doctor)
Companion Bonnie Langford (Melanie Bush)
Richard Briers — Chief Caretaker / The Great Architect
Clive Merrison — Deputy Chief Caretaker
Elizabeth Spriggs — Tabby
Brenda Bruce — Tilda
Judy Cornwell — Maddy
Howard Cooke — Pex
Julie Brennon — Fire Escape
Annabel Yuresha — Bin Liner
Catherine Cusack — Blue Kang Leader
Astra Sheridan — Yellow Kang
Joseph Young — Young Caretaker
Simon Coady — Video Commentary
Writer Stephen Wyatt
Director Nicholas Mallett
Script editor Andrew Cartmel
Producer John Nathan-Turner
Executive producer(s) None
Production code 7E
Series Season 24
Length 4 episodes, 25 minutes each
Originally broadcast October 5–October 26, 1987