It is the summer of 1971. Dr. Philip Zimbardo launches a study on the psychology of imprisonment. Twenty-four male undergraduates are randomly assigned to be either a guard or a prisoner. Set in a simulated jail, the project unfolds. The participants rapidly embody their roles -- the guards become power-hungry and sadistic, while the prisoners, subject to degradation, strategize as underdogs. It soon becomes clear that, as Zimbardo and team monitor the escalation of action through surveillance cameras, they are not fully aware of how they, too, have become part of the experiment.