The story is about a two week psychological experiment conducted to observe how a group of men would behave when given roles as guards or prisoners in a make-shift prison cell. The rules state that anyone can quit anytime, no violence is allowed and money is only given to all those who make it to the end of the experiment.
Quite scary to see how the guards slowly start to abuse their authority while the prisoners have to endure the stress of living in a cell! Realised that it is based on the true story only after watching the film!
Internet Movie Database Link