Tarek (Moritz Bleibtreu), a taxi-driver, comes across a newspaper ad calling for volunteers for an experiment lasting 14 days. He visits the University Psychological Institute where Dr. Jutta Grimm (Andrea Sawatzki), the scientific assistant for the project, explains that it involves role-playing in a prison-like setting. The 20 participants will be divided into groups of guards and prisoners. She adds that those who take part will be required to give up their private life and their rights as citizens.

Tarek, who is also a journalist, decides his involvement would make a great undercover story. His former employer, a newspaper editor, agrees. Tarek obtains a pair of glasses implanted with a tiny camera so he can record crucial evidence of what transpires in the mock prison scene. Later that night, not concentrating on his driving, he plows into another car driven by Dora (Maren Eggert), who is returning home after her father's funeral. They spend an evening together, sharing stories from their lives and having sex.

Tarek reports to the Institute very excited about his new adventure. Professor Thon (Edgar Selge), who designed the experiment, tells the 20 men that during the two weeks they will learn to apply pressure and bear pressure. Tarek is convinced that the best way to make it through is to treat it as a game. He lands in a cell with an electrician (Wotan Wilke Moehring) and Steinhoff (Christian Berkel), an aloof introvert. The guards have been told that they are to keep order but cannot use violence. Tarek tests the waters with a protest against Eckert (Timo Dierkes) after this guard forces a prisoner to drink milk even though he is allergic to it. Tarek and his two roommates are forced to do push-ups. He then ups the ante when he realizes that Berus (Justus von Dohnanyi) is the most rigid and tyrannical of the guards. He pushes him and soon the two are in a dangerous battle of wills with the safety of everyone else in jeopardy. It doesn't help that Tarek has a burning hatred for all authority figures because he was humiliated as a boy by his cruel father.

Oliver Hirschbiegel directs this riveting German drama that brings to mind the psychological intensity of Cube. The screenplay is based on the novel Black Box by Mario Giordano. In his famous psychological study conducted at Yale in the 1960s, Stanley Milgram showed that ordinary people in situations of "normal" obedience to authority would do things contrary to decent or humane behavior. This film also touches on that theme. We are challenged to ponder the ethical firepower of power and the human propensity to rebel against those above them.

It is easy to sit back in the comfort of our homes and judge the violence in the many hotspots around the world. It is quite another thing to witness a movie like this one and to realize that there is within each one of us a monstrous guard who given the opportunity could revel in the chance to hurt others.