For Lynne Ramsay, motives are vague, sometimes unknowable things.

In the Scottish director's films — three features, including the new "We Need to Talk About Kevin — characters act out awkwardly and unpredictably, baffled and nullified by deadly predicaments that are, in some measure, their own making.

A young woman walks away from her suicide boyfriend and heads to Spain, taking credit for his unpublished novel ("Morvern Callar"). A boy's rough-housing secretly drowns a playmate in blighted 1970s Glasgow (the exceptional "Ratcatcher").

Guilt doesn't just weigh heavily, it obliterates.

"We Need to Talk About Kevin," Ramsay's first film in nearly 10 years, is about a woman wracked by the trauma of having mothered a mass murdering teenage son. Eva Khatchadourian (Tilda Swinton) is a suburban wife to a cheerful, oblivious husband, Franklin (John C. Reilly), whose waking nightmare is enforced by constant flashbacks, mulling over her mothering of Kevin (as a teen, played by Ezra Miller) from infancy and up until the fateful high school massacre.

It is, to be sure, a parent's horror story. The origin of this real-life demon is traced back to birth and even earlier, pondering the arrival of a bad seed and his subsequent nurturing.

The film opens in ominous tones with a younger Eva at the La Tomatina festival in Valencia, where she and the masses are covered in blood-like tomato. Back in present day (in which Eva is alone, desolate and slightly unkempt), she remains splashed in red, only it's her house vandalized in revenge with red paint. (Red and tomatoes are a recurring motif.)

Eva makes her way grimly through her days. She's ostracized by the townspeople, some of whom simply walk up to her on the sidewalk and smack her. She's managed to land a job as a clerk in a travel agency, having previously been a globe-trotting travel writer.

Swinton, a moviegoer's pleasure even in darkness such as this, plays Eva as meekly resigned to her desolation. When religious advocates ask her whether she knows where she's going in the afterlife, she answers certainly that she's going to hell: "Eternal damnation. The whole bit." It's a riveting, layered performance and one that pairs interestingly with hers in "The Deep End" as a deeply protective mother.

How did things go so off the rails? The flashbacks show Eva's unease in pregnancy, staring fearfully at the bare bellies of fellow mothers-to-be. She wistfully recalls happier, more liberated days in New York City before Franklin, against her wishes, led her to the suburbs. Even at birth, she's advised by the doctor to "stop resisting."

When the baby comes, they seem mismatched from the start. Eva can't keep him from screaming, but Franklin somehow soothes him immediately. As a toddler, Kevin has already formed his fierce, manipulative opposition, refusing to say "mommy" and calling her "dumb."

Eva's attempts at motherly care — cold though she is — are eventually beaten down and she breaks, at one point seething: "Every morning mommy wakes up and wishes she was in France." In another moment of weakness, she turns violent.

By the time Kevin is a teenager, he's a smart, cynical, vulgar, sneering sociopath. He remains sweet to his blissfully unaware father, who calls him "Kev" and — tragically — greases his interest in archery. In a role that inevitably pulls toward horror cliche, Miller is believably nihilistic: "There's no point. That's the point," he says.

The script by Ramsay and Rory Stewart Kinnear, adapting Lionel Shriver's acclaimed novel, artfully blends these two timelines evoking Eva's interior consciousness, where every moment recalls a precursor to the tragedy, a debate of her role in it.

The visually gifted Ramsay and cinematographer Seamus McGarvey give the movie an ethereal, atmospheric feeling, aided by Jonny Greenwood's pulsating score. At times, the film swaps Eva for Kevin: How much of Eva is in Kevin? And vice versa? The focus blurs in and out.

The structure of the film leads it on a track that can't go anywhere but where it must: The massacre at the school. But leading suspense toward the fateful scene is dramatically unsatisfying. That it happened, which was long ago established, isn't the reveal "We Need to Talk About Kevin" needs. It's a pursuit of "why," the answer to which the film fails to grasp.

Perhaps this is as it should be: The formation of such a monster can only be a mystery. But this thoroughly well-crafted, if rigidly conceived film could use a little more talking — at least some therapy! — about Kevin.

"We Need to Talk About Kevin"

Grade: Two and a half stars out of four

Running Time: 112 minutes

MPAA Rating: R