Although its plot suggests a psychological thriller, “Moka, ” a new film from the Swiss director Frédéric Mermoud, mostly plays as a character drama with a long fuse. Its opening minutes constitute a quiet cinematic sonata of loss and grief, showing Diane (Emmanuelle Devos) lying in bed and smoking, visited by visions and flashbacks of her teenage son, Luc, who was killed in a hit-and-run. Months later Diane is still beside herself, partly because the driver hasn’t been identified, let alone caught.
To that end, Diane has hired a private eye, who has compiled a portfolio of possible cars and descriptions of drivers in Évian, France, where the auto accident happened. Diane takes the ferry there from her home in Lausanne, Switzerland, and eventually fixates on a coffee-colored Mercedes (the movie’s title derives from the hue of the car) and the two people who drive around in it, a salon owner, Marlène, and her lover, Michel.
As played by Nathalie Baye, Marlène comes off as shallow yet enigmatic, with a big satisfied smile she has engineered for her customers and her intimates. She’s a stark contrast to the tortured Diane. As Diane follows her and peers at her from her car, the viewer can almost see the grieving mother constructing an awful narrative around Marlène. That notion continues to grip Diane as she insinuates herself not only into Marlène’s life, but also that of Michel, and of Marlène’s daughter from a prior relationship. Diane’s obsessive quest for closure has brought out a certain native cunning in her, but she’s also dangerously naïve — she asks her private investigator to furnish her with a gun, which he doesn’t even entertain. She receives more cooperation from a young drug runner working the Lake Geneva ferry, leading to a flirtation with criminality that provides a momentary distraction from sorrow.
Something has to give, obviously, and the movie’s climax has sufficient twists and turns for a conventional payoff. But the movie, adapted from a novel by Tatiana de Rosnay, is ultimately more concerned with the genuinely tragic dimensions of the story than its suspense angles. That point is driven home with a final scene that is likely to move audience members to tears, just as it does Diane. “Moka” is also a first-rate showcase for two of French cinema’s finest actors, Ms. Devos and Ms. Baye, both of whom do career-high work here.
An earlier version of this review reversed the cities where the main character, Diane, travels to and from to investigate her son’s death. She travels to Évian, France, from Lausanne, Switzerland.