20 volunteers agree to take part in a seemingly well-paid experiment advertised by the university. It is supposed to be about aggressive behavior in an artificial prison situation. A journalist senses a story behind the ad and smuggles himself in among the test subjects. They are randomly divided into prisoners and guards. What seems like a game at the beginning soon turns into bloody seriousness.

20 men are chosen to participate in the roles of guards and prisoners in a psychological study that ultimately spirals out of control.