The Rani, needing the Doctor's expertise, shoots down his TARDIS, crash-landing it on planet Lykertya where the Doctor dies and subsequently regenerates. She biochemically induces selective amnesia before disguising herself as Mel in order to angle him deceptively into repairing one of her broken machines. The real Mel? Left behind in the TARDIS, alive but unconscious, where she's found by a grim rebel Lakertyan who then makes off with her.
The Rani's deviousness inadvertently sets the Doctor and Mel against each other - she having yet seen the Doctor in his new regeneration, he believing Mel is the Rani disguised, and each thinking the other is an agent of utmost evil to be brought down. Two unanswered questions linger: Why has the Rani collected geniuses, and why is she messing around with "strange matter."
The solstice nears, making it time for the Rani to bring her plans into fruition. The Doctor's sympathies for Beyus, ruler of the Lykertyans, are rather qualified. Beyus' heart is for his people yet something prompts him to collaborate fully in helping the Rani reach all her objectives. The answer, he's told, lies within the Center of Leisure.
The Rani, at last, links the Doctor into her great brain machine, the crowning jewel in her component packet of geniuses brought together to turn Lakertya itself into one vast cerebral mass capable of redirecting time anywhere in the universe, giving her absolute power over all creation.
The Doctor and Mel visit Paradise Towers, a apartment complex in the 21st century, only to find it rat-infested and ruined. Paradise Towers is inhabited by Rezzies (elderly women, at least some of whom are cannibals), Kangs (roving gangs of teenage girls), Pex (a cowardly young warrior who proclaims himself the local hero) and Caretakers led by a Chief whose job is to keep the apartment complex in order. But the Doctor and Mel find that robotic cleaners are killing off everyone in Paradise Towers, one-by-one. The culprit is Kroagnon, the building's award-winning ...
The Doctor reunites with the Red Kangs to question why no one questions the steady number of deaths at Paradise Towers. Elsewhere, Mel meets the Blue Kangs who reveal that Pex, the lone young male in the complex (who talks a good game while flanking Mel), is not nearly the heroic and capable fighter he continually boasts of being.
The Doctor discovers that Paradise Towers' great architect, Kroagnon, was also responsible for Miracle City, an infamous killer habitat. Though chance circumstances permit Mel to avoid a dinner date with a couple of grandmotherly cannibals, the Doctor realizes everyone must band together or be destined for the menu of a greater infamy lurking in the basement.
Meeting up at the pool, the Doctor leads the surviving Rezzies, Kangs and Caretakers as they draw the line together on the 245th floor against the systematic cleansing of all life by Kroagnon and his robotic Cleaners.
The Bannermen have successfully wiped out all but the last of the Chimeron - Delta, the queen, no less. She escapes with an egg and boards an intergalactic bus of Navarino vacationers heading for 1959 Earth to visit Disneyland. On that bus is Mel, followed closely by the Doctor in his TARDIS.
The Bannermen are coming to Earth thanks to a signal from an opportunistic bounty hunter recognizing Delta. DIsneyland is safe due to a collision with a satellite that redirects the vacationers to the Shangri-La Holiday Camp in South Wales. There, the camp mechanic is smitten by the Queen Delta and her newly hatched green baby.
The Doctor's party rallies to the house of an elderly beekeeper where the young Chimeron princess hits another growth spurt that reveals the reason why the Bannermen want the Chimeron wiped out. Meanwhile, Gavrok sets a deadly booby-trap right outside the Doctor's TARDIS, and Billy makes a heedless and irrevocable decision.
In Iceworld, a trading port on the dark side of planet Svartos, the Doctor chances across Sabalom Glitz and joins him on a treasure hunt in the frozen caverns of the planet where a dragon is rumored to resides. Meanwhile Mel and a recently fired waitress named Ace run afoul of Kane, the icy director of Iceworld, whose frozen touch means death.
While Mel and Ace run from Glitz's former crewmen (whom he sold to Kane), officers Belazs and Kracauer conspire to overthrow Kane. The Doctor, meanwhile, discovers there really is a dragon in the ice caverns, which turns out to be a bio-mechanoid with a very interesting function.
At last learning the location of the missing key to his spaceship, Kane has the dragon hunted down and Iceworld brutally purged of all visitors; but, the Doctor, visiting the Ice Garden, learns something significant that will put the chagrin on Kane's grand plans for home world vengeance.