The Doctor and Romana’s holiday in Brighton is brought to a sudden end when K-9 takes in sea-water and explodes. They instead venture to the Leisure Hive of Argolis, a holiday complex built by the surviving Argolin following their devastating war with the Foamasi. As ever, they arrive at a point of crisis in the year 2290. The Leisure Hive is facing bankruptcy and the Argolin’s Earth agent, Brock, arrives with his lawyer Klout, bearing an offer to buy the planet outright. Regrettably the offer is from the Foamasi, the only species that could live on the radiation-infused surface of Argolis, and so the Argolin Board will not consider it. Hit by the shock of events, the ageing Board Chairman Morix succumbs to a rapid death – the Argolin war curse of advanced cellular degradation – and his consort Mena is declared the new Chairman.
The Doctor is intrigued by the manipulation of the tachyon in the Hive’s Tachyon Recreation Generator, which is the main tourist attraction and is able to duplicate and manipulate organic matter. He witnesses the Generator kill a human tourist after it has been sabotaged, the latest in a series of acts of wilful damage.
No sooner has Mena returned to Argolis than her own body clock begins to speed up. Earth scientist Hardin has been brought to Argolis to help her and her people by using time experiments to rejuvenate a people rendered sterile by the war of forty years earlier. Recognising the value of scientists, she engages the Doctor and Romana to help Hardin with his work. The time travellers know Hardin has been faking his work, but Romana also feels the experiments should have worked.
The death of Hardin’s assistant, Stimson, is pinned on the Doctor and the Time Lord is forced into the Generator as a trial of sorts. After further sabotage he emerges five hundred years older—an old man with flowing white hair. Pangol, Mena’s son, is the most warlike and vindictive of the Argolin and interprets this as proof of guilt, ordering the Doctor and Romana to be confined. Hardin frees them to help him in his experiments.
Foamasi government agents now make themselves apparent on Argolis — and unmask Brock and Klout as doppelgangers in bodysuits. In truth they are of the West Lodge Foamasi, a criminal faction which made the buyout offer for Argolis and has been sabotaging the Hive to help their negotiations. The agents place them under arrest and prepare to depart.
Pangol now usurps his mother as leader of the Argolin, declaring to Brock and the Board that he is the first of the new Argolin: a product of cloning experiments conducted in the recreation generator. This, he contends, is the future of the Argolin, who will use the Generator to recreate themselves and rise up again. As a skilled tachyon engineer he starts to clone himself in the Generator, creating hundred of Pangols in battle-dress and ready for conflict. The Doctor interferes in the tachyon manipulation with three happy consequences: Pangol’s clones become unstable and disappear, and he is reduced to the age of a baby; Mena is rejuvenated and saved from death; and the Doctor himself loses the added centuries. The only cost is the Randomiser—it had been fitted in the TARDIS to prevent the Black Guardian tracking it—which the Doctor loses in the Generator.