The title of “Moka,” an elegantly lean, low-temperature thriller from Swiss writer-director Frédéric Mermoud, turns out to be less enigmatic than it sounds: It’s the color — a neutral, creamed-coffee hue of 1970s vintage — of the car responsible for the unseen hit-and-run that sets its intriguingly hesitant revenge plot in motion. That’s a fitting name for a film that paints largely in subtle, in-between shades, as grieving mother Emmanuelle Devos finds herself torn between impetuous fury and more calculated psychological warfare in tracking down those responsible for her teenage son’s death. A Chabrol-like slow burn more concerned with fine character crinkles than grand narrative revelations, this Locarno premiere is complicated considerably by Devos’ ever-astute, ambiguous presence; though it’s more sleek than sensational, “Moka’s” classical genre impulses give it a shot at international distribution.

From “I’ve Loved You So Long” to last year’s “Zurich,” grief over the loss of a child has become something of a stock character motivation in Euro arthouse cinema of late. So it’s to the credit of “Moka” — crisply adapted and relocated from a novel by Frenchwoman Tatiana de Rosnay, whose work also yielded the Kristin Scott Thomas hit “Sarah’s Key” — that, amid its other opacities, the film makes little attempt to conceal the tragedy driving Diane Kramer (Devos) into shadowy moral territory.

Following a terrifically tight, wordless opening sequence that sees Diane escaping from a Lausanne sanitorium — to which she has evidently been committed following a nervous breakdown of sorts — viewers should swiftly piece together the essentials. Her violin-prodigy son Luc (Paulin Jaccoud, glimpsed in taciturn visions and flashbacks) was recently struck dead by the driver of a Mercedes coupe still unidentified by police. Unconvinced (rightly, it turns out) that they’ve been thorough in their investigations, and with little support from her more accepting, increasingly estranged husband Simon (Samuel Labarthe), she enlists a private eye to do some digging of his own.

It doesn’t take him long to turn up a few leads — the most compelling of which takes Diane across Lake Geneva to the famed spa town of Évian. There, she becomes convinced she’s found the offending vehicle: A cherished classic belonging to middle-aged beautician Marlene (a bleach-blonde Nathalie Baye) and her buff fitness-instructor boyfriend Michel (David Clavel). If they love the car so much, why is it suddenly up for sale? And why has the paintwork been newly touched up on the bonnet? Approaching Michel in the guise of a prospective buyer, Diane’s suspicions soon turn to seething, resentful certainty.

It would seem, then, that the whodunnit portion of proceedings is over before it’s even begun — yet strangely, it’s once the mystery is more or less solved that “Moka” begins to get really interesting. With her prey effectively caught, Diane is nervously ambivalent over what to actually do with it. Playing for time while also fueling a morbid fascination with the uninterrupted lives of her son’s accidental killers, she strikes up separate, sustained acquaintances with Michel and Marlene, who respond to her neighborly stalking with wary bemusement.

As Diane maintains a fragile double life between Lausanne and Évian — its hovering halves separated by the aptly mist-blanketed lake — the film largely forgoes its more Hitchcockian properties for febrile, intuitive character study, beautifully served by Devos’ witty, coolly disciplined performance. That we’re never quite sure if the tentative bond Diane forms with Marlene is entirely performed on the former’s part — or if she has indeed reluctantly discovered common ground with her affable sworn enemy — is among the richest complexities of the actress’s work, while Baye (on far slyer form here than in Xavier Dolan’s recent shriekfest “It’s Only the End of the World”) responds in kind with a performance of equivalent masking and layered politesse.

Watching these two fine actresses circle each other in a kind of watchful alligator’s tango, each waiting for the other to blink first, is the chief pleasure on offer in “Moka”: When Diane sunnily tells her unwitting target that she “still looks great for [her] age,” the sharp release of passive aggression is almost gasp-inducing. Not every subplot here is handled with quite such scalpel-wielding finesse, though a public burst of frustration against Simon’s placating behavior offers a startling glimpse of the protagonist’s otherwise deftly managed personae in involuntary collision. Diane’s shady affiliation with scuzzy-sexy drug dealer Vincent (Olivier Chantreau), meanwhile, arms the plot with its obligatory loaded weapon, but also contributes the film’s more hackneyed genre notes: In a film otherwise adept at splintering serene surfaces, we hardly need his character to tell us, “Looks can be deceiving.”

Mostly content for his actors to calibrate the tension between them, Mermoud’s directorial intrusion is confidently minimal. The tasteful classical refrains of the score gain in cruel resonance as the backstory is uncovered, while the sober tones and cashmere finish of Irina Lubtchansky’s lensing announce a sense of calm begging to be ruptured. But it’s the finer particularities of the sound design — beginning with the arresting opening shot, as Diane taps her head against a plate-glass window to an escalating tempo and volume — that provide our most immediate conduit into the protagonist’s divided headspace.

Film Review: ‘Moka’

Reviewed at Locarno Film Festival (Piazza Grande), Aug. 3, 2016. Running time: <strong>90 MIN.</strong>

  • Production: (France-Switzerland) A Diligence Films, Bande à Part Films, Tabo Tabo Films, Sampek Prods. production, in co-production with Radio Télévision Suisse, in association with Sofitvciné, Cofimage 2. (International sales: Pyramide International, Paris.) Producers: Damien Couvreur, Julien Rouch, Jean-Stéphane Bron, Tonie Marshall. Executive producer: Adrian Blaser.
  • Crew: Director: Frédéric Mermoud. Writers: Mermoud, Antonin Martin-Hilbert, adapted from the novel by Tatiana de Rosnay. Camera (color): Irina Lubtchansky. Editor, Sarah Anderson.
  • With: Emmanuelle Devos, Nathalie Baye, David Clavel, Diane Rouxel, Samuel Labarthe, Olivier Chantreau, Jean-Philippe Ecoffey, Marion Reymond, Paulin Jaccoud. (French dialogue)