About one of the most controversial experiments in the history of psychology, invoked to shed light on everything from the abuse of prisoners at Abu Ghraib, to prison rioting and police brutality. In 1971 Professor Philip Zimbardo recruited students to play prisoners or guards in a makeshift jail to examine the nature of good and evil. Due to last two weeks, within days four prisoners suffered breakdowns and a fifth was on hunger strike. With testimony from the original participants, the film uncovers why the behaviour of all involved, including its instigator, became so extreme that the experiment had to be abruptly terminated in less than a week.