Charlotte Rampling depicts a woman’s mental deterioration following her husband’s apparent drowning with stunning authenticity in “Under the Sand.” Her subtle, nuanced performance is easily the most striking thing in Francois Ozon’s fourth film. As a whole the picture is a typically French mixture of angst and ambiguity, with elements of both a ghost story and a thriller, but it’s actually more a character study along the lines of Roman Polanski’s “Repulsion” (though it eschews the gore and mayhem of that still-shocking effort). Measured, moody and obstinately enigmatic, it makes for sometimes enthralling, sometimes infuriating viewing; but Rampling’s deeply felt turn gives it a center that makes it consistently intriguing.

When we first meet Marie and Jean Drillon (Rampling and Bruno Cremer), they’re beginning their vacation at a country house near the coast, but there’s soon a brooding Gallic indication that circumstances are hardly idyllic: as Jean strolls through the neighboring woods collecting wood for a fire, he turns over a fallen log, and the camera focuses in on the worms, ants and other beasties crawling beneath it–an image which is obviously intended as emblematic of the frailty of existence (and perhaps a sign of Jean’s own morose state). Soon the couple is on a desolate beach, and as Marie sleeps Jean goes off for a swim; when she awakens, she finds that he’s disappeared. She quickly contacts the authorities, who initiate a search, but it’s all to no avail. Marie eventually returns home to Paris and resumes her duties as a literature teacher, but it soon becomes clear that she’s unable to deal with loneliness. Scenes with her concerned friends show that she’s acting as if Jean were still alive; she’s initially reluctant to connect with Vincent (Jacques Nolot), a publisher introduced to her by her friend Amanda (Alexandra Stewart), and when she returns to her flat, she’s visited by Jean–whether he’s real or a fantasy is deliberately left unclear. Meanwhile Jean’s elderly mother implies that Jean simply left because he was tired of Marie. And although she finds herself in financial straits because her husband’s fate can’t be definitively determined, when the police finally locate a body that might be Jean’s, Marie avoids contacting them to attempt an identification.

There are elements of “Under the Sand” that recall George Sluizer’s “The Vanishing” (the fine 1988 Dutch original, not the awful 1993 English remake), but it quickly becomes apparent that Ozon’s not interested in generating much suspense about what happened to poor Jean Drillon. His focus is on Marie’s inability to come to terms with loss and move on; and the ending, which is so vague that it still leaves all the options open, brings no more closure to the audience than it does to her. But while ultimately the picture is somewhat frustrating as simple narrative, Rampling’s extraordinary performance makes it a powerful depiction of grief. None of the other cast members come near to matching her; the two men in her life, Cremer and Nolot, are merely stolid by comparison, though Andree Tainsy makes a vivid impression in her cameo as her vinegary mother-in-law. Otherwise the show is simply Rampling’s, and thankfully Ozon, while hardly the most imaginative of directors, gives ample room for her performance to breathe.

“Under the Sand,” like a great many recent French films, will prove too chilly, detached and clinical for most U.S. viewers, and it doesn’t match the best work of Patrice Leconte or Claude Sautet, One can rejoice, though, that it provides a challenging star vehicle for the still-underappreciated talents of Charlotte Rampling. And that she seizes the opportunity so such great effect.