The Doctor and Romana are on vacation in Brighton—the Doctor has been trying to get there since Leela was his companion—but the TARDIS has arrived in the wrong season and they are freezing on the beach. K9 chases a ball into the surf and shorts out. That got him out of the way for a while. They move on to the Leisure Hive of Argolis, built by the Argolins after a devastating 20-minute nuclear war with the Foamasi forty years ago. But the Leisure Hive is nearly bankrupt and their Earthborn agent Brock (John Collin) and his lawyer Klout (Ian Talbot) are there offering to buy the planet. It is their enemy the Foamasi making the offer and the Argolins refuse. The Doctor studies the manipulation of the Hive’s Tachyon Recreation Generator, which can duplicate and manipulate organic matter. But there is sabotage and cellular degradation and death everywhere inside the dome protecting them from the deadly atmosphere outside. The Chairman Morix (Laurence Payne) dies.
The new Chairman Mena (Adrienne Cori) finds her own body aging quickly because of the radiation from the war. Earth scientist Hardin (Nigel Lambert) is there to use time experiments to help people rendered sterile by the war. The Doctor and Romana are asked to help him, though they know he has been faking his results. But someone is murdered and naturally the Doctor is blamed. Romana and Hardin perfect the time experiments and bargain for his freedom. But the Doctor is selected to test the procedure. The machine malfunctions and he ages 500 years, coming out looking like that famous self-portrait by Leonardo DaVinci. Still sharp, however, he realizes that recreation is re-creation and the machine can generate clones.
Pangol (David Haig), the youngest Argolin, is performing dangerous experiments. Brock and Klout bring a new offer from the West Lodge, a criminal group who want Argolis as a base of operations. Brock and Klout are Foamasi impersonators. The Doctor takes the randomiser from the TARDIS and attaches it to the recreation chamber to destabilize the device, hoping to put it out of operation.
Romana tries to warn Pangol not to use the generator but fails. The Foamasi shuttle is destroyed by Pangol, who then uses the generator to produce an army of tachyon replicas of himself in armor to rebuild the Argolin race in his image and make them great again. Romana is to be put outside, on the deadly surface. But the tachyon replicas are merely rejuvenated Doctors. When they take off their helmets, they are all him. Rangol re-enters the generator, but the machine is set to rejuvenate and cannot be stopped. When he emerges, he is a baby. Though Romana advises against it, the Doctor leaves the randomiser attached to the recreation generator, which will likely leave the TARDIS vulnerable to the Black Guardian.
Foamasi is a kind of anagram of Mafioso. John Leeson returned as the voice of K9, though he was used less and less. The aged Doctor was something of a triumph of makeup and acting skills. Ian Talbot’s portrayal of Klout got him in the cast list despite his having no dialogue, but he was creepy and unsettling without uttering a word. John Nathan Turner took over as producer and instituted reforms, cutting the humor, scaling back K9, redesigning the Doctor’s scarf and coat in burgundy, and (to Tom Baker’s disgust) putting question marks on his outfit, which remained through three more Doctors until the series ended in 1989. The ITV premiered Buck Rogers in the 25th Century opposite the first episode of the Leisure Hive. This was the first time they had scheduled another science-fiction show opposite Doctor Who and the series never really recovered. And Tom Baker’s and Lalla Ward’s marriage was falling apart. I am wondering if this was not the beginning of the end for Doctor Who. The series seemed to get no respect from the BBC after that.