Paradise Towers two elderly residents ("rezzies") live. Tilda and Tabby explain that all the able-bodied men left the Towers to fight a war, leaving behind only children and the elderly. The only other man still loose in the Towers is Pex, a would-be hero, who appoints himself Mel's guardian. At the Caretaker control centre, the Doctor meets 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 cites an imaginary rule from the Caretakers' manual, confusing them enough to make his escape. Mel and Pex meanwhile have
Paradise Towers Doctor heads off to investigate and 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 felt human beings would ruin his creation and so placed multiple deathtraps throughout the