Make no mistake about it, Polisse is a genuine curate’s egg. A rough, raggedy portrait of an under-pressure Parisian Child Protection Unit, it scorches an unpredictable trail from harrowing to laughable and back again in just over two unremitting, frequently melodramatic hours. In fact, it’s difficult to think of another film in recent years in which the good and the truly awful have coexisted in such close proximity.

Utilising a primarily hand-held, documentary-style aesthetic, director Maïwenn plunges us into a world where harried individuals must confront acts of unspeakable depravity on a daily basis. They are a tight-knit team prone to bickering (about anything from linguistics to gender politics) and airing their dirty personal laundry at voluble levels. The comrades’ badinage-under-duress vibe is impressively established in Polisse‘s early stages, and the film has an earthy, punchy compelling start. Sadly, as subplots pile up at a rate of knots, it swiftly begins to lose focus.

One of Maïwenn’s least wise decisions was to cast herself in the role of a roving photographer commissioned by the ministry to capture the unit’s actions. She’s less a character, more an ethereal, slightly distracting presence: the film equivalent of an Enya song coming on your radio. The group’s debating about the merits of the her role is – in script terms – clumsily self-reflexive, but at least brings her character into some sort of focus. Her burgeoning romance with the CPU’s hot-headed Fred (played by rapper-turned-actor Joeystarr) is totally uninvolving, soap-opera stuff.

A number of scenes are excoriatingly powerful as lone entities, but such is Maïwenn’s lack of tonal and structural control, they tend to exist in a vacuum. One particularly harrowing passage in which a young African boy is separated from his mother would be just as effective if viewed separately. Likewise, a late showdown in which a Muslim CPU member challenges a suspected sex offender over his knowledge of the Koran seems to have been included simply because the subject of faith hasn’t been explicitly brought up yet.

There’s also a forced levity that sits oddly with such decidedly bleak material. A tense raid on a sect of child-criminal groomers is immediately followed by a jaw-droppingly weird dance sequence on a school bus, set to disco music. And these guys don’t go to the pub to unwind, no; instead they’re granted a full-on, City of God-style nightclub tear-up. Elsewhere, we’re treated to snatches of bleak gallows humour; witness the scene when the crew fall around laughing at a gauche young girl who’s been dispensing oral sex in return for a smartphone, and another where disappointment is registered at catching a dull case (“Can’t we do a rape or a gang rape?” grumbles one character). It’s in these moments of dark observation where Polisse recalls The Wire (the landmark HBO show to which it’s been rather unconvincingly compared). Unlike David Simon’s show, though, it never gets to grips with the labyrinthine menace of institutions on any meaningful level; authority figures are summarily cast as two-dimensional husks.

There’s too much effective stuff in this messy film to write it off as a total failure. The grainy aesthetic is apposite, and the performances are generally strong across the board. Furthermore, in its own weirdly shambolic way, Polisse does a good job of painting the embattled CPU as some kind of living, gasping organism composed of raggedy, interdependent human parts, ploughing a thankless furrow in a bleak urban landscape.

However, it’s the combination of fundamental structural problems and constant recourse to hysterical melodrama which really derail things. As the film rushes headlong into an overwrought denoument (which will surely be parodied for years to come), the realisation hits you that there’s been no real narrative arc to speak of; you’ve just been beaten over the head for two hours from all angles. Narrative strands repeatedly pop up, then disappear without trace, often making it extremely difficult to follow what’s going on. It makes you appreciate the skill of, say, (the late) Geraldine Peroni and Dylan Tichenor (editors on multi-character opus’ Short Cuts and Magnolia respectively) who knew exactly when to pick up one story and leave another.

If one was to be generous in the extreme, one might suggest the film’s wayward form was designed to mirror the chaotic interior lives and profession of its characters. But that would be pushing it big time. Polisse would have made a compelling TV series, allowing space for themes and characters to flourish. As it is, it registers as a weird, passionate, misshapen lump of a film which simply has way too much going on, marshalled with nowhere near enough skill.

Polisse is in cinemas now.