Volunteers enter an underground facility and are asked to spend three weeks in a mock-up prison, playing out the randomly alotted roles of convicts and guards. But it soon becomes evident that the guards are taking their roles too seriously.
Inspired by an actual 1971 experiment, this opens as cool, psychological drama. Undercover reporter Fahd needs the study to get out of hand to make his story sexier, so he needles mild-mannered 'guard' Berus, an incipient megalomaniac who eventually asserts his authority by imprisoning psychiatric staff who try to limit his power.
Claustrophobia and the opportunity for apparently consequence-free brutality turn the prisoners into shuffling wrecks and the guards into strutting thugs. A jolly Elvis impersonator becomes a bullying rapist, while a military man intent on quietly serving his time is forced to bond with Fahd to stage a jailbreak.
Echoing the mock-doc feel of Blair Witch, director Hirschbiegel takes his time with the set-up, cutting away to what seems at first the irrelevance of Fahd's new girlfriend on the outside, before delivering an unforgettably suspenseful second half.
A symphony of psychological and physical horrors.