A Prophet, Jacques Audiard, 149 mins (18)

Jacques Audiard's latest isn't merely a brilliant prison drama – it's also a terrifying vision of a universally corrupt France

(Picselect)

You'll have heard already that Jacques Audiard's A Prophet is an extraordinary prison movie, and that's true. But more than that, it's a film about education. A Prophet follows a gauche young man through the French prison system, until he becomes the man walking taller and tougher in the film's teasingly ambivalent final shot.

The film begins with 19-year-old Malik (Tahar Rahim), sentenced to six years in prison for an unspecified crime. Shaggy, shambling and battered, the young Arab is only just starting his apprenticeship of violence and humiliation. No sooner is he behind bars than he's ordered by the jail's ruling Corsican gang to carry out a murder. The terrified Malik is eager to get the whole business over with – except that his designated victim, Reyeb (Hichem Yacoubi), wants to sit and talk, advising the illiterate youth to start making something of himself.

Even after Malik has carried out his bloody mission, Reyeb continues to offer him good counsel. Every now and then, he'll appear in ghostly form to keep his killer friendly company – with fire playing over him like a human flambé, or with cigarette smoke oozing from the gash that Malik has put in his neck.

This blackly hallucinatory streak runs with bracing incongruity through what is otherwise a realistic, extremely hard-bitten crime story. It traces Malik's ascent through the criminal universe, starting as gofer to the Corsican mob under Luciani (Niels Arestrup). Malik becomes an adopted Corsican, although his racist patrons despise him, while the prison's Arab contingent regards him with suspicion. An Arab with no sense of Islamic identity, and even less of a personal past, Malik floats between two worlds. Becoming a crafty autodidact, Malik manoeuvres himself into Luciani's confidence, eventually carrying out a series of perilous missions during 12-hour leave periods, while also building his own power base.

Once Malik starts his sorties into the outside world, the film has both picked up a thunderous narrative momentum and begun to stretch plausibility: suddenly, Malik is flying to Marseille as a diplomatic envoy to hostile mobsters. While the film's final third is a sleek gang thriller that bowls along briskly enough to suit Brian De Palma, Audiard's real achievement is his evocation of the enclosed prison world, in which there's no visible authority other than the ruling gang.

Malik comes to this world a clueless child, emerges from it a Machiavellian prince. As Malik, Tahar Rahim heads a cast consisting largely of unknowns, many of them real ex-prisoners. What makes Rahim such a compelling lead is the enigma that he manages to sustain till the end – as if Malik isn't a fully formed personality, only an endlessly adaptable organism that reacts creatively to whatever fate throws at it. Manipulative, self-serving, yet innocent in contrast to those around him, Malik is unglamorous, sometimes abject, but brimming with the energy of a born survivor.

Rahim wins us over with gentle charisma, introverted intensity and the sheer stamina that the role demands. He's superbly matched by Niels Arestrup as Luciani, a professional actor who looks as authentic as anyone here; exuding endlessly corrupt world-weariness, like Dennis Hopper with Brando's bulk, Arestrup's air of lofty contempt suggests a thug king close to the end of his reign.

A Prophet is unfailingly brilliant in detailing the prison world. Audiard's team – including art director Michel Barthélémy and cameraman Stéphane Fontaine – creates a harshly vivid jail environment that's actually a set although you would easily believe it was real, with its distressed walls and comfortless spaces. You can almost smell the piss and despair.

Audiard's film is a culturally provocative statement, given France's anxiety about the visible signs of Islamic identity. And by making its anti-hero a whip-smart Arab criminal on the make, who plays Muslims against mafiosi, A Prophet offers as much of a barb to Islamic as to European sensibilities. The film further suggests that there's no real law in France, just a reign of universal corruption in which the man who uses his wits may emerge looking purer than his peers – may come, indeed, to be taken as a prophet.

Compelling and immensely watchable though A Prophet is, I can't help feeling it misses the concise edge of previous Audiard films such as Read My Lips or The Beat That My Heart Skipped. There's so much incident crammed in here that the film constantly threatens to burst its bounds – as if this isn't the definitive edited-down version but an extended director's cut that Audiard has gone ahead and released. And the background gang intrigues are utterly perplexing. Still, this is a film of considerable brilliance that contrives to get us root-ing for a man who, in his time, is a betrayer, a plotter, a willing stooge – and makes him emerge as a heroic figure. In the end, you feel that A Prophet is only incidentally about the education of a criminal, and fundamentally about the making of a politician.

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