The Changeling Years (short story)

Summary
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.

Characters

 * Fourth Doctor
 * Leela
 * Brenda Jones
 * Harry Jones
 * Wulfren
 * Harold Scorfe
 * The Director
 * Prolon slaves

Continuity

 * The Daleks also ran tests to learn why they were always defeated by humans. (TV: The Evil of the Daleks)
 * The War Lords also recreated different time periods. (TV: The War Games)