This movie from first-time feature director Ladj Ly has one of the most striking and even glorious pre-credit sequences I can remember. It shows the cheering, screaming crowds on the streets of Paris last summer, when France had just beaten Croatia 4-2 in the World Cup. This is a seething mass of humanity with tricolours waving everywhere, boiling with joy. Finally, the director flashes up the title over the people, ecstatic in their triumph: Les Misérables.

It’s an irresistible irony and it kicks the film off with a great exhilarating jolt of humour, cynicism, energy and savvy. But what begins as a fascinatingly tough cop procedural gets less interesting when the violence begins, and it becomes a solemnly ponderous issue movie on those familiar subjects of police brutality and community divisions. The stakes are ostentatiously raised, the riot makes it looks like a war movie and it ends unconvincingly. Rather as with Jacques Audiard’s Dheepan from 2015, it’s a movie that builds to a confrontation that isn’t satisfying dramatically (although Dheepan was the Cannes Palme D’Or winner).

Facebook Twitter Pinterest Confronting issues head on ... Ladj Ly. Photograph: Eric Feferberg/AFP/Getty Images

The setting is the tough Montfermeil district in the east of Paris, known for its violent banlieue Les Bosquets, and also for being the location of the Thenardiers’ inn in Victor Hugo’s novel Les Misérables. Stéphane (Damien Bonnard) is a cop who has just joined the street crime unit’s day patrol, alongside Gwada (Djibril Zonga) and under the command of the notoriously cynical, reactionary and streetwise Chris (Alexis Manenti), who gives Stéphane’s debut a real Training Day feel. Their job is simply to cruise around, a visible demonstration of the law, not hesitating to chat, to establish a breezily and superficially friendly relationship with the community, and to cultivate informants – but also to go in hard against anyone they suspect for any reason: Chris loves to “frisk” attractive young women at bus stops.

Stéphane soon sees that the power structure on the streets, and within his unit, is very complex: Chris’s power over him and Gwada is maintained by exhausting stream of banter and bullying, and there is a fascinating cameo from Jeanne Balibar as their chief, who establishes a very similar flirtatious relationship with her low-ranking subordinates. Chris’s own authority outside is created via a kind of trusted local, nicknamed “The Mayor” (Steve Tientcheu) who manages the market stalls in a semi-corrupt way and is a de facto police community liaison person. But the cops must also negotiate their relationship with Salah (Almamy Kanouté), a reformed jihadi who owns a kebab shop and commands great respect with the hair-trigger young men. The police rely on Salah’s goodwill, or at any rate his impassive neutrality. In the case of a real threat of violence, the officers have “less-lethal” Flash-Ball guns that can be fired terrifyingly and deafeningly into the air.

The film’s ambient mood is initially very good: there is a terrific easy swing to the action as the cop car barrels through the streets, stopping periodically to bust someone’s balls, or for the cops to bust each other’s balls – and this is a very male world. “Like Miss France, all I want is world peace,” says Chris, jauntily. But then there is a bizarre mishap: a lion cub is stolen from a travelling circus run by Gypsy travellers who, having suspected a local boy, bust out the N-word in their confrontation with the Mayor – and it is down to our three anti-heroes to find the lion cub and save Montfermeil from a gigantic race riot. But their heavy-handed policing makes the situation very much worse, and then they realise they are being filmed by a drone belonging to a local kid.

Pre-violent normality is where this movie is at its strongest: just the day-to-day, hour-by-hour experience of being out on the streets, feeling the simmer of something that might escalate but probably won’t. After all, Paris and all France are loved up by the World Cup. A smaller-scale dramatic situation within this mesh of racial and ideological tensions might have worked better. But the colossal conflagration becomes paradoxically less exciting, and the tang of black comedy vanishes when real bloodshed appears. The director may want to confront these issues head on – the racism and violence just below the surface. Indeed, raising it above the surface is the point. But much of the drama and humanity get blitzed by the molotov cocktails.