A young woman (Astra Sheridan), the last surviving member of a gang known as the yellow Kangs, is killed in the corridors of a huge tower block called Paradise Towers. The Doctor and Mel arrive in the TARDIS, Mel hoping to take a dip in the Towers’ swimming pool, but find that the building is run down and defaced with graffiti. They are captured by the red Kangs (Christina Clark, Louise Clifford, Helen Fung, Elizabeth Gardner, Nisha Nayar, Julietta Norde, Jennie Slade, Martha Stylianou, Roberta Wells, Lottie Winter) and the Doctor makes friends with their leaders, Bin Liner (Annabelle Yuresha) and Fire Escape (Julie Brennon). The Kangs decide to take the two travellers to their ‘hide-in’, but they are attacked by Caretakers (Sean Bowden, Andrew J Bush, James Carrington, William Perrie, Nick Santini, Don Weinstein, Rupert Clive, Barrimore) and the Doctor is arrested. 

Mel escapes and meets two old ladies, Tilda (Brenda Bruce) and Tabby (Elizabeth Spriggs), known as rezzies. The old ladies are friendly, offering her tea and cakes, but her stay at their apartment is interrupted by a young man named Pex (Howard Cooke) who breaks down the door in order to ‘save’ her. She leaves, and Pex insists on accompanying her to protect and guide her. 

The Doctor is taken to meet the Chief Caretaker (Richard Briers), who believes him to be the Great Architect responsible for creating Paradise Towers and orders a 327 Appendix 3 Subsection 9 death for him. The Doctor escapes by tricking his guards into following non-existent rules. 

Mel and Pex – the only young man left in the Towers when all the others left to fight a war – are captured by the blue Kangs (Suzanna Cardash, Tanya Davidson-Jones, Iona Dean, Harriet Eedle, Leigh Funnell, Heather Mair Thomas, Liz Wood). The Doctor meanwhile finds his way back to the red Kang ‘brain-quarters’, where he is recaptured by the Caretakers and in turn rescued by Bin Liner and Fire Escape. 

The Chief Caretaker visits a mist-shrouded area in the basement of the building and speaks with something that proclaims it is hungry. The Chief Caretaker calls it his ‘pet’ and refers to himself as its ‘daddy’. 

Mel manages to talk her way out of the clutches of the Blue Kangs. She then encounters Tabby and Tilda again, but their friendly facade vanishes as they wrap her in a shawl and threaten her with a toasting fork, apparently intent on eating her. She escapes when first Tabby and the Tilda are dragged into their apartment’s waste disposal outlet by a robot arm that emerges from within it. A large robot cleaner transports the bodies of the two old ladies to the thing in the basement. 

Mel and Pex make their way to a lift and, after many failed attempts, finally arrive at floor 304 where the pool is situated. Mel intends to go swimming, failing to notice that there is a bright yellow cleaning robot in the water. 

The Doctor postulates that the Kangs’ parents trapped the Great Architect, Kroagnon, in the building to stop him from completing it. The Kangs reveal that there is a ‘door with smoke’ in the basement. The Doctor, Fire Escape, Bin Liner and Air Duct (unknown) prepare to go and investigate. Before they can do so, however, the Blue Kangs attack, their Leader (Catherine Cusack), claiming that they have won the game. The Doctor intercedes and gets the two groups of Kangs to work together. 

The Chief Caretaker is escorted to the basement by a robot cleaner and again talks with the mysterious creature. The Doctor, Fire Escape, Bin Liner, Air Duct and the Blue Kang Leader arrive. They watch as the Chief Caretaker is forced to stand under a tube but are then attacked and chased away by robot cleaners. When they have gone, the tube retracts to reveal that the Chief Caretaker has now been taken over by Kroagnon. 

Mel is attacked by the cleaning robot in the pool. Pex is too scared to help her, but she grabs his gun and destroys the robot. The Doctor gathers all the Kangs together and takes them to the pool, where he is reunited with Mel. 

As Kroagnon systematically ‘cleanses’ the floors of Paradise Towers by having the cleaning robots kill all the inhabitants, the remaining rezzies, including Maddy (Judy Cornwell), and caretakers, including the Deputy Chief Caretaker (Clive Merrison), also arrive at the pool. The Doctor gets everyone to work together to try to defeat Kroagnon. 

The Deputy Chief Caretaker explains that on floor 245, Sodium Street, corridor 75, there is a store of explosives that they can use to destroy the cleaners. The Doctor plans to set a trap for Kroagnon and Pex volunteers to lure him there. When they arrive, the Doctor tries to topple Kroagnon into the mined store but is unable to do so. Pex plucks up courage and pushes Kroagnon in, but falls in after him. The store explodes. 

The Kangs hold a ceremony to celebrate Pex’s life and apparent death. The Doctor is made an honorary Kang – red and blue – and he and Mel leave in the TARDIS. On the wall nearby is a graffito reading ‘Pex Lives’.

_{Synopsis from Doctor Who: The Seventh Doctor Handbook by David J. Howe, Mark Stammers and Stephen James Walker, reprinted with permission; further reproduction is not permitted. Available from Telos}