“Stranger By the Lake” opens Friday at Sundance Cinemas. Not rated, (contains explicit sexual content), 1:37, three and a half stars out of four.

“I’m not sure it’s allowed here.” “It’s not allowed anywhere.”

The sliver of  beach in rural France is an idyll for gay men, both closeted and open. They come, remove their clothes, stretch out in the sand, or go for a swim. Little is said on the beach. But, eventually, most of them go up into the woods for a stroll, and find each other there.

“Stranger by the Lake” is not for everyone, with explicit sexual content that makes “Blue is the Warmest Color” look like “A Walk to Remember.” But see past all the fumblings in the bushes, and writer-director Alain Guarardie’s film reveals itself as a chilling psychological drama about the limits of desire, and the attractiveness of self-destruction.

Franck (Pierre Deladonchamps) is a boyish man who spends his days on the beach. He befriends shy Henry (Patrick d’Assumcao), so uncomfortable in his own skin he keeps his shorts on and arms resolutely folded, as if trying to will himself to have a good time. But Franck is more drawn to Michel (Christophe Paou), handsome, tan and arrogant.

One evening at twilight, Franck spies on Michel and his lover swimming in the lake alone. They roughhouse, and the roughhousing turns violent. Soon, only Michel is seen above the surface. Franck knows he has probably just witnessed a murder. But instead of calling the police, Franck becomes Michel’s lover, and the fear he feels that he may be Michel’s next victim ends up only being a further turn-on.

Watching “Stranger by the Lake,” I kept thinking how, in another context, the film has the plot of a Henry James novel. A young ingenue spurns the advances of a safe suitor, instead falling for a disreputable character and is ruined as a result. In a way, the movie is the inverse of a Victorian novel, where passions burn deep within the carefully cultured manners of its protagonists. Here, sex is free and easy, as common among strangers as exchanging pleasantries. But love is just as elusive.

Guarardie seems fascinated with the social rituals of the cruising spot — watching the half-clothed men wander through the tall grass, looking for an anonymous mate, looks like some bizarre mating ritual from a nature documentary. That’s the purpose, I think, of the sexual explicitness — Guardardie doesn’t want to arouse, he just wants to get it right. And there’s comedy here, too, in the form of an exceedingly polite voyeur with his pants down, or one beach patron who draws elaborately arbitrary borders between which parts of the beach allow cruising and which do not.

Aside from a suspenseful climax, “Stranger By The Lake” moves at a languid pace that’s fitting for a beachside film. But there’s a disquiet under that lazy, hedonistic reverie; is Michel only taking the “anything goes” philosophy of this sanctuary to murderous extremes? And Franck, who doesn’t seem to understand his own desire, finds himself drawn to that kind of freedom, even if it costs him his life.