The progression of director Kathryn Bigelow's career has been intriguing. Her early career saw her direct, amongst others, the best vampire movie ever in Near Dark, and the excessively silly but persuasively enjoyable Point Break, before arriving at the troubled recent American history. The Hurt Locker was a fascinating Iraq War drama that drilled into the psyche of a bomb disposal officer; while Zero Dark Thirty took on the even more contentious subject of the CIA's search for Osama Bin Laden. For her latest film she takes on the '67 Detroit riots, focusing her film down to an incident of police brutality at the Algiers Motel. The outcome is a fascinating watch, messily sprawling, narratively unsatisfying, politically urgent.

Initially the film doesn't appear to have a fixed narrative, beyond chronicling the Detroit riots in a docudrama style. We see the moment that sparked the riots with the shutting down of a speakeasy; we follow a Motown band as they prepare for their big break; we witness police brutality that foreshadows where the film will end up. All of this through cinematographer Barry Ackroyd's roving, intimate camera. It is an interesting start, giving Detroit an unpredictability, but also a messiness that makes it tough to engage with. The film finds its focus and slowly morphs into a sweat-drenched, laser-focused horror set in the Algiers' corridors and it is here when the film truly flourishes. The fact the film continues after these proceedings to show their impact is less satisfying then it has the potential to be. But when the film is good, it is one of the most necessary of the year.

Proceedings are held together by a trio of exceedingly strong performances, from a talent-rich ensemble. John Boyega plays a security guard dragged into the incident depicted; Will Poulter heads up a group of police officers responsible for the excessive force and extreme outcomes; and Algee Smith is one of the victims of the unfolding events. Much of the heavy emotive lifting is down to Smith, who is at first effortlessly charming then heartbreakingly broken. Boyega brings a moral complexity to a figure who finds himself an outsider to all parties; it is certainly his strongest performance to date. But it is Poulter's portrayal that lingers, compellingly vile and with enough hints of grey as to avoid caricature. A fascinatingly grounded performance in a role that could so easily be overplayed.

Detroit is a film held back by the fact that, at its core, the material it presents would make a very worthy short TV series or a taut two-hour film. Here it is both too long to satisfy as a thriller and too short to do the story justice. Releasing the film as a summer release feels like an absurd choice. It is a work of art that is spiky, difficult to unpack. To play it alongside the popcorn and candyfloss of competing films and not in the autumn months, when it feels better suited to achieve the award attention it deserves, is strange. But the film itself, though messy, is never less then compelling, and has some of the finest performances of the year.