We Need to Talk About Kevin, Lynne Ramsay, 112 mins (15)

Lynne Ramsay's We Need To Talk About Kevin begins with a beautiful, ominous image – a gauzy curtain floating in white light.

It sets the note for a film that is elusive, somehow impalpable – which is odd for a story about blood, rage and bodily excretions.

Promoting Kevin in Cannes, its lead Tilda Swinton said that on reading Lionel Shriver's novel, she immediately thought that Ramsay was the one person who could film it. Personally, the director strikes me as the least obvious candidate, and that's what makes the film interesting. Shriver's Kevin – about a woman coping with the terrible crime of her teenage son – is an analytically cool, ironic contemplation of the nature/nurture question and of parents' inability to understand their offspring. Acute as it is, this engrossing but stylistically functional novel feels like journalism in disguise, neatly proffering its subject for further discussion: the consummate upmarket book-club book.

Ramsay, however, thinks not in concepts but in images. She doesn't make intellectual films, but ones that are close to music, taking visuals to the point of abstraction – as in her debut Ratcatcher, about a Glasgow childhood, and the eccentric Oban-to-Ibiza jaunt Morvern Callar.

Shriver fans may be startled to see how much leeway Ramsay – with co-writer Rory Stewart Kinnear and editor Joe Bini – has given herself in telling a story. A flow of flashbacks and reveries, Ramsay's hyper-fragmented film isn't an adaptation of the book in the usual sense, more an impressionistic remix. The story's horrific climax isn't quite omitted but is treated so telegraphically that it seems to be happening backstage. It's as if Ramsay is thinking between the lines of the book, rather than filming those lines themselves.

Swinton plays Eva, once a successful travel writer. We learn this from a bravura sequence at a Spanish tomato festival, as a pulp-slathered Eva crowd-surfs ecstatically over a heaving, scarlet-smeared throng – establishing the film's red leitmotif and telling us indirectly that There Will Be Blood. There's more red when Eva wakes, years later, to find that someone has covered her house with paint. It's the first in a series of indignities that this solitary, emotionally demolished woman has to face. People contemptuously slap her in passing or break her eggs at the supermarket, and the intrepid globe-trotter now has to grovel for a menial job at a cheapskate travel agent's.

What went wrong with Eva's life? Maternity, we discover. Against her inclinations, Eva had a child with husband Franklin (John C Reilly). Little Kevin starts as a baby screaming loud enough to compete with Manhattan roadworks, then becomes a sullen tot (chilling three-year-old Rock Duer) who literally refuses to play ball with Mommy. As he grows older (equally unnerving seven-year-old Jasper Newell), Kevin devises various tricks to confound Mom – turning her office walls into a Jackson Pollock or filling at will the nappy he still wears. The cruel twist is that affable Dad can't see that there's a problem.

Later, Kevin is played by androgynous, faintly Gothic teenager Ezra Miller, whose enigmatic half-smirk suggests dream casting for Young Caligula. With the entry of Miller, and his decidedly creepy beauty, the relationship between mother and son becomes more perverse, implicitly sexual – an evening out resembling a bad date between an anxious older woman and a scarily self-possessed younger man.

The film is strongest in the interplay between Eva and the various Kevins. At other times, Ramsay is more interested in visual possibilities as she digresses, sometimes mesmerisingly, into dream-like images of the everyday: a Halloween parade, a brightly coloured pile of crushed breakfast cereals. Ramsay and cinematographer Seamus McGarvey make full use – sometimes too full use – of the blood-red theme, but the film's masterstroke is to use the bland cleanness of the family home as a frame for dirty, ugly, unmanageable feelings.

Where Kevin goes askew is in its picture of America – particularly at Eva's new workplace where everyone is a goonish hick. True, we're seeing suburbia through the eyes of Eva, an urbane cosmopolitan brought to earth with a crash. But the cartoon grotesquerie feels condescending, and I couldn't buy the soundtrack use of wheezy antique country and western.

The mystery in the film is not so much what made Kevin a monster (if that's what he is), more how much Eva recognises the monster in herself. Swinton's taut nerviness – her Eva looks as if she's seen rougher times than Christ in a Flemish altarpiece – speaks volumes about a woman who's spent her life fleeing the company of lesser mortals. Increasingly we realise that Kevin's mission is to rub her face in her own universal contempt; he's a domestic version of Batman's Joker, a grim satirist holding up a black mirror to his mother's worldview.

Seeing Kevin a first time, one immediately rejoiced in the return of one of British film-making's genuine free spirits. On a second viewing, the flaws are more apparent – this elliptical work doesn't congeal into the more intensely troubling whole that it promises. But a straight take on Shriver would have been a flatter, familiar thing. Frustrating as it is, this is a Lynne Ramsay film to the hilt. It's not the Kevin you know, and it may not be the Kevin you want – but if you see it, you'll certainly need to talk about it.

Next Week:

Jonathan Romney faces belles and bullets in Mexican drama Miss Bala

Film Choice

The BFI London Film Festival continues until Thursday with Rachel Weisz providing swoons of post-war passion in Terence Davies's closing film The Deep Blue Sea. Other highlights include Sokurov's Venice prize-winner Faust, Sean Penn's goofy Goth turn in This Must Be the Place and Rhys Ifans take on the Shakespeare story in Anonymous.