Dr. Philip Zimbardo wants to experiment with the reason why people turn "Evil". So he decides to make a fake prison at Standford university.
Some students sign up for the experiment and some go through the procedures of being arrested. They are taken into a real police station and are then blindfolded and taken to the fake prison.
Some students are chosen to be prisoners and some are chosen to be guards. Everything is well with the prisoners, although they aren't used to how the guards treat them, they all keep thinking "It's just an experiment".
Only after 2 weeks the guards begin to mistreat the prisoners and constantly harass them in anyway they can and the prisoners begin to think that the prison isn't part of the experiment.
The prisoners begin to lose their minds and actually believe that they are in a real prison. Some begin to adapt to the prison lifestyle, the prison guards keep being harsher and harsher on the prisoners.
Dr.Zimbardo watches the whole thing and ends the experiment after 2 weeks. The prisoners were having mental breakdowns, a sadism outbreak and a hunger strike and Zimbardo was forced to shut the experiment down before something worse could happen.