On the surface Kathryn Bigelow’s “Detroit” is a period piece, a docu-dramatic account of the so-called Algiers Motel incident of July, 1967, which was in many respects the culmination of the riots that engulfed the city for days. As such the film, made with the pulsating intensity for which Bigelow has become famous, is harrowing—though also infuriating not only because of the palpable sense of injustice it so vividly portrays but because of its preference for visceral impact over dramatic nuance. Though it depicts an incident fully half a century old, moreover, the film inevitably carries contemporary overtones, since it forces one to consider the extent to which a general attitude of racial prejudice, especially as evidenced in recent cases reflecting mistreatment of African-American citizens by the police, continues to prevail, even if in less blatant form.

The film begins with a breathless dramatization of the seemingly trivial episode that set off the riots on July 23—a police raid on an impromptu after-hours club in a black neighborhood where a group was celebrating the return of two Vietnam War vets. Unable to take the arrested crowd out through a back door, the cops paraded them out theatrically onto the street, provoking the ire of onlookers. The anger spiraled out of control, and eventually the local police will eventually be reinforced by state cops, National Guard troops and federal army contingents.

After a brief prologue about the “Great Migration” northward and the black experience in cities like Detroit, Bigelow and her collaborators, production designer Jeremy Hindle and cinematographer Barry Ackroyd, skillfully restage this beginning of the so-called 12th Street Riot. Then Mark Boal’s script splits into several threads that will eventually link up at the Algiers, periodically enhanced with archival footage used to provide context.

One thread involves a trio of cops led by Philip Krauss (Will Poulter), a trigger-happy racist who prowls the streets looking for looters to shoot, and does in fact kill one of them. (His submissive colleagues Demens and Flynn are played by Jack Reynor and Ben O’Toole.)

Another concentrates on Larry Reed (Algee Smith), lead singer of a aspiring singing group called the Dramatics, whose big opportunity at a variety show is quashed when the Fox Theatre is closed down because of the street violence; he and the group’s manager Fred Temple (Jacob Latimore) find refuge at the motel, where they eventually link up with a couple of white girls, Julie Ann (Hannah Murray) and Karen (Kaitlyn Dever), and a roomful of brothers that includes high-strung Carl Cooper (Jason Mitchell).

Meanwhile Melvin Dismukes (John Boyega), a serious security officer at a store near the motel, makes contact with a squad of guardsmen stationed nearby.

It’s at this point that Carl begins playing around with a starter pistol, first pretending to shoot one of his friends and then firing out the window, leading the guardsmen to believe they’d come under attack. They respond, along with the cops led by Krauss, and storm the motel annex. The terrified Carl is shot trying to flee, but the others—including Robert Greene (Anthony Mackie), a veteran caught in his room—are arrested. They’re not hauled off to jail, though. Krauss, obviously terrified at the thought of adding Carl’s death to his record, pins them up against the wall and threatens them all with death unless they reveal where the gun is. What follows is a horrifying display of police brutality and racial bigotry as Krauss and his fellow cops take several of their prisoners away and pretend to kill them in order to force the others to give them the information they want to justify their actions. Melvin, who has entered the scene with the guardsmen, tries to lessen the tension but fails, and another man winds up dead, in what amounts to a grisly accident.

The standoff comes to an inconclusive end, but still more evidence of racism emerges when Melvin is indicted, along with Krauss and his fellow officers, in the incident. Their trials form the final act of the film, and given what has proceeded the outcome is not likely to offer much confidence in the American justice system.

There will undoubtedly be disagreement over the historical accuracy of Boal’s script. Many of the details, especially in the more intimate moments, are clearly speculative, and many of the characterizations have been fashioned for optimal effect (the fact that some names, most notably those of the policemen, are changed is evidence of that); this is, after all, a drama based on fact rather than a documentary. To be honest, subtlety is in short supply: the story is told in stark, frenetic terms that often make nuance difficult. Similarly, most of the acting cannot be said to be much more than serviceable. Though everyone contributes more than adequately to the ensemble, only a few—like Poulter and Smith—stand out for the vitality they bring to their roles, even if (as in Poulter’s case) sometimes in one-note form. Other fine actors, like Boyega and Mackie, underplay to a great extent, not only providing the film with contrast but conveying the need their characters feel to at least appear deferential. Most of the others fall between the two poles.

One cannot doubt the sincerity and commitment that Bigelow and her colleagues have brought to this story. “Detroit” is an impassioned piece of work, expressive of the same attitude of righteous indignation that permeated many message films of the fifties and sixties—even if it was more placidly presented, as in “To Kill a Mockingbird.” It has flaws, but they are faults that can be forgiven in view of the film’s sheer cinematic power, as well as its historical significance and topical relevance.