Alain Guiraudie's L'Inconnu Du Lac, or Stranger by the Lake, is a stunning, confrontationally explicit psychological drama set at a French lakeside cruising spot for gay men. He creates an atmosphere of absolutely frank homoeroticism, utterly without inhibition or taboo. I was reminded of Alan Hollinghurst's The Swimming Pool Library or Thom Gunn's poem The Discovery of the Pacific. But when a single, terrible event takes place, the mood swings to that of classic Hollywood suspense, like John M Stahl's Leave Her to Heaven (1945) or George Stevens's A Place in the Sun (1951), movies in which a beautiful lake becomes the epicentre of danger.

Christophe Paou plays Michel, a handsome, well-built man who comes to the lake and is instantly enamoured of Franck, played by Pierre Deladonchamps, who has already struck up a tender, platonic friendship with Henri (Patrick d'Assumçao), a fat, lonely and unhappy guy who sits by himself, away from the others.

This nexus of relationships is placed under intense scrutiny when the police are called in to investigate a certain terrible event. An inspector finds himself perplexed and frustrated by the cruising credo: guys who are into voyeurism should make good witnesses, but those who don't ask each other's names or phone numbers, guys who cultivate a willed forgetfulness about yesterday's experience so as to prepare the way for the next contact – they are creating a cloud of unknowing, highly injurious to a police investigation. Guiraudie's sheer frankness about sex is refreshing: far away from any prurient Joe-Eszterhas-type erotic danger. It is an almost pastoral scene, which makes the single violent act, and the reaction to it, so disturbing.

• This article was corrected on 7 March, as Pierre Deladonchamps's character was misidentified as Michael.