The late Claude Chabrol might be smiling from above at the thought that his mantle has been taken up so skillfully by writer-director Alain Guiraudie, who brings the older filmmaker’s characteristic mood of quiet menace in a cultured environment to this tale of lust and murder at a remote lakeside that serves as a gay cruising ground—a story with elements that are also reminiscent of the narrative style of Patricia Highsmith.

In a series of leisurely widescreen tableaux exquisitely shot by Claire Mathon, the film opens on a sunny summer’s day, introducing Franck (Pierre Deladonchamps), a handsome young man, as he parks, saunters through the woods to the beach, takes off his clothes and wades into the lake for a swim. Other men wander about through the trees or along the shore looking for signs from sunbathers or like-minded wanderers that a quick assignation might be in order. Noticing an overweight, unattractive older man sitting apart from anybody else, Franck swims back and joins him for some small talk. It turns out that the fellow, Henri (Patrick D’Assumcao), is a recently divorced vacationer who’s not looking to score but enjoys Franck’s company. Franck’s attention is diverted, however, when he spies Michel (Christophe Paou), a well-muscled guy with a major mustache, and is instantly intrigued by him. He follows Michel into the woods, only to find him engaged with another man, and exits the scene even as others are eying him.

During the following days, the three men settle into a pattern, with Franck and Henri conversing and Franck watching Michel until he takes a chance and introduces himself. That brings a reaction from another fellow who appears to be Michel’s jealous boyfriend and leads him off into the woods. That doesn’t deter Franck, however, who begins obsessively to observe the two until he sees something awful—the pair engaging in some horseplay in the water that turns into an apparent confrontation in which Michel drowns the man.

Franck’s reaction, however, is to grow even more impassioned over the thought of Michel. While continuing to talk with Henri—conversations that touch on loneliness, sex and obsession—he approaches Michel again and the two quickly are engaged in intense activity beneath the branches. What he’s witnessed haunts Franck, but though he questions Michel gingerly about the missing man, the killer is nonchalant—until the body is discovered and a police inspector (Jerome Chappette) shows up, asking questions. A thin, reedy fellow with unusually expressive hands, he prods both men to give him information, but they—along with the other regulars—offer no answers. Meanwhile Franck grows increasingly needy, wanting more than sex from Michel; but Michel refuses, saying that he needs to be discreet. And the tension between them, exacerbated by the inspector’s intrusions, begins to fester.

“Stranger by the Lake” isn’t a whodunit, of course—we’ve seen Michel commit the crime, just as Franck has. But it is a mystery, one concerned with larger issues of human needs and motives, addressed both through Franck and Henri’s colloquies and through the portrayal of the erotic rituals of searching, refusal and acceptance that the men circling one another in the forest perform. Why does Franck place himself in obvious danger in pursuit of fulfilling an obsessive, inexplicable desire? What drives paunchy, depressed Henri to come to the beach day after day, though he never evinces a desire to connect sexually with Franck or anyone else, and doesn’t even take a swim or go au naturel, as virtually all the other habitués of the lakeside idyll do? Still more generally, the film ruminates on the relationship between sex and death, something made especially acute by being situated in a gay environment where unprotected sex is the norm for some while terrifying others.

In the final reels, Guiraudie takes a more conventional turn, especially with the police investigation, which naturally causes a rift between Franck and Michel that invites Henri’s protective side. But even here anyone looking for a comfortably realistic denouement will be disappointed; this is a film of questions, not answers, and it maintains its oblique, suggestive character to the very end. It’s extremely graphic in its depiction of acts of sexual intimacy, which some may dismiss as pornographic in all but name. And its occasional flashes of mordant humor—particularly in scenes involving a voyeur (Mathieu Vervisch) who masturbates while watching panting couples but who’s uncommonly considerate of those who object, and genteel after actually engaging with another human being—will unsettle some viewers rather than bringing a nervous smile to their lips.

But Guiraudie observes it all with almost clinical detachment, as though performing anthropological research on an exotic culture that always remains as tantalizingly out of reach of our understanding as some objects of desire on the beach do from those who cast desperate glances at them. This is an extraordinarily atmospheric, unsettling film that raises mysteries that, in the end, remain defiantly insoluble.