The Doctor and Leela arrive on Earth in what appears to be an industrial complex. While Leela is captured, the Doctor discovers that it is the site of a sociological study in which different societies in different time periods are recreated by conditioning volunteers into believing they are different people. Their goal is to learn why previous alien conquests of Earth had failed by determining the essential strengths and weaknesses of the human race, then selling the information. Leela encourages the test subjects to fight their captors, and the Doctor shuts down the machines in the control centre.
- The Doctor was on his way to the British Museum. He later recalls Alcatraz while breaking into a building with his sonic screwdriver.
- The complex is patrolled by helicopters and contains machines such as a neural scanner and a Gersataski scan. They employ Prolons, natives of Prolix IV who had been called in to deal with the Portland riots of 2217.
- Among the time periods recreated include the 1st century and the 20th century.
- The company running the study is not named, and the local government is only referred to as "The State". The inner cities are said to be "depressing".
- A brain scan conducted on the Doctor shows that he is insane.
- Prolix IV is said to be in "Monocros", but this is probably a typographical error of "Monoceros" (a real-world constellation).