The Doctor has taken Peri to Bryce's Asteroid, home of the "greatest market" with wonderful merchandise. However, he finds that the market has changed since he last visited. It now sells body parts and other scientific equipment. They talk with a stall owner named Elspeth, who tells them that this is the Lifemarket, which sells anything one needs to create life.
The Doctor is appalled and wants to see someone in authority. Therefore, he begins destroying Elspeth's stall to attract police attention. He and Peri are taken to the Grand Auctioneer, who thinks the Doctor is a malfunctioning dead body and sends him to the workshop. Meanwhile, he takes Peri on a tour and tells the story of his life. He has been exiled from his home planet, Bryce, because he discovered the secret of reanimating dead cells. He bought a part of Bryce's Asteroid and set up the Lifemarket to prove to the leaders on Bryce that they need his services.
The Doctor finds himself in the workshop and sees five dead bodies labelled Military Hardware. Suspicious, he begins to work.
The Auctioneer takes Peri with him to meet with a client named Mr Carrington, who manages a pop group named Military Hardware. The Auctioneer takes them to see the finished work, the reanimated dead bodies of the group. However, the bodies start to destroy objects and attack people, having been reprogrammed by the Doctor who thought they were part of an invasion plan.
The stall owners have either fled or been killed. The dead members of Military Hardware have been destroyed, and Mr Carrington promises that no one in the music industry will ever do business on the Lifemarket.
Peri explains to the Doctor that Military Hardware was a music group, not an invasion. The Doctor still thinks that what the Auctioneer was doing was wrong. As he and Peri leave, Peri suggests that the Auctioneer take up topiary, at which he is very good.
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