“The Stanford Prison Experiment” plays like the most unnerving improvisational theater game imaginable.

In 1971, social psychology professor Philip Zimbardo set up a two-week study in the basement of a Stanford University campus building in order to prove one of two things. One: The brutality and dehumanization in a prison setting was dispositional, tied to the personalities of the prison guards and the prisoners. Or two: The brutality was situational, an inevitable product of the prison hierarchy and culture itself.

In his fake prison, Zimbardo and his colleagues cast one group of undergraduate Stanford males as the guards, another as the prisoners. The students earned $15 a day and were encouraged, even required, to play it for real. They were promised by Zimbardo it wouldn’t get too rough. But it did. The experiment escalated quickly, turning violent, unpredictable and, from Zimbardo’s viewpoint, extremely compelling, even if its ethical basis was made of sand.

Previously the subject of several documentaries and countless term papers on ethics, the correctional system and other matters, the notorious experiment is now a fictionalized film directed by Kyle Patrick Alvarez and based on “The Lucifer Effect: Understanding How Good People Turn Evil,” Zimbardo’s 2007 book.

Alvarez establishes a calm, dispassionate tone at the outset, using his camera for efficient, orderly lateral maneuvers down the hallway, as the pecking order in this pretend incarceration nightmare is established.

Michael Angarano, a smart actor rarely cast in menacing roles, is excellent as the kid playing the head guard, who is nicknamed John Wayne by his overseers. Inventing punishments and verbal taunts with the skill and enthusiasm of Strother Martin in “Cool Hand Luke,” this tyro drives the study into some dangerous corners.

Billy Crudup plays Zimbardo, and Olivia Thirlby becomes the film's conscience as Zimbardo’s ex-student, current lover and eventual wife. (The real-life couple are still married.) Crudup has no interest in making Zimbardo come off nobly. If anything, this de facto academic warden edges close to being a better-dressed variation on Charles Manson, all wild, unblinking eyes and ferocious devotion to the experiment going out of control. It’s a matter of simplification in the name of drama. The rest of the actors are very good, chief among them Nelsan Ellis (“Get on Up”) as an ex-con brought in by Zimbardo to legitimize the project.

These days, Zimbardo delivers popular talks on the psychology of evil, retelling the story of his morally dubious Stanford experiment to audiences all over the world. The film’s version of events makes it seem comically obvious: It never should have been approved in the first place and never should have gotten past the first day. This has a mixed effect on the movie itself, which inevitably fights against its own sense of dulled outrage and methodical role-playing. But it’s pretty gripping all the same.

‘The Stanford Prison Experiment’

Three stars

out of four stars

Rated R; language, abusive behavior, sexual references

2 hours, 2 minutes