Stanford University psychology professor Philip Zimbardo conducts a Stanford prison experiment to test the hypothesis that the personality traits of prisoners and guards are the chief cause of abusive behavior between them. In the experiment, Zimbardo selects fifteen male students to participate in a 14-day prison simulation to take roles as prisoners or guards. They receive $15 per day. The experiment is conducted in a mock prison located in the basement of Jordan Hall, the university's psychology department building. The students who are guards become abusive, as does Zimbardo himself, as they immerse themselves in their assigned roles. Two students who play the role of prisoners quit the experiment early due to psychological meltdowns, and, only after being chastised and roughly brought back to reality by his girlfriend, Christina Maslach, Zimbardo abruptly stops the entire experiment after only six days.