A group of men volunteer to participate in a psychological study focusing on the effects of perceived power and control. They are divided randomly into two groups: prisoners and guards. Among them is Travis, an idealistic, peaceful man, and Barris, a meek individual who takes on the role of a guard. As the experiment commences, the guards are tasked with maintaining order without physical force, and the prisoners are instructed to follow basic, non-punitive rules. However, tensions quickly arise as the guards begin to exercise their authority more aggressively, driven by a sense of superiority and control. Travis, among the prisoners, starts challenging the increasingly harsh rules, leading to a struggle for dominance between the two groups.

Gradually, the line between experiment and reality blurs. The guards, led by the once timid Barris, become more sadistic and authoritarian, while the prisoners, led by Travis, are subjected to humiliating and dehumanizing treatment. Neither the participants nor the researchers intervene as the situation spirals out of control, highlighting the alarming ease with which ordinary people can be swayed into cruelty when placed in positions of unchecked power. The study's initial aim disintegrates as real human suffering takes over, testing the limits of societal structures and individual morality.