Moderately risky liaisons

French writer/director Catherine Breillat continues to catch us off guard with her latest, “The Last Mistress.” In earlier films, she shocked us either with extremely explicit sex-cum-violence (“Anatomy of Hell”) or with sudden explosions of mayhem that seemed to come from nowhere (“Fat Girl”). This time she shocks us by, well, not shocking us — which is a roundabout way of saying that this may be the Breillat film for people who can’t stand Breillat films.

To date, her features have almost all been from original screenplays; her very few adaptations have been based on the prose work of ... Catherine Breillat. But this time around, she has adapted a novel by 19th-century writer Jules-Amédée Barbey d’Aurevilly (filmed at least once before for French TV).

The central character here is Ryno de Marigny (Fu’ad Aït Aattou), who is in the process of breaking up with his longtime mistress, Vellini (Asia Argento), to clear the deck before marrying the notably younger (and “purer”) Hermangarde (Roxane Mesquida, the Parker Posey look-alike who also played the “pretty sister” in “Fat Girl”). When Hermangarde’s grandmother, the Marquise de Flers (Claude Sarraute, a writer making her film acting debut at 80) is informed that Ryno has recently been seen exiting Vellini’s house, she demands an explanation of his situation.

Ryno relates the history of his relationship with Vellini in a flashback that occupies more than half the movie. An incurable rake, he initially dismisses her as “that ugly mutt” ... loud enough for her to hear. Not surprisingly, she seems to loathe him; as a result, she almost instantly becomes his object of obsessive desire. Despite her marriage to an ancient British nobleman with an occasional resemblance to Willie Nelson, Ryno pursues her to the point of assault, sparking a duel challenge from the geezer.

That does the trick: Ryno allows himself to be shot, thereby triggering Vellini’s passion. Much to the attending physician’s dismay, even before the bullet is removed, Vellini sensuously, creepily licks Ryno’s wound — presumably fishing for a metaphorical reciprocation. The two take off together to North Africa, where they spend several years. They even have a little girl, but her sudden demise turns their relationship from gold to dross.

Ryno admits to the Marquise that, while the love has long since evaporated, passion has repeatedly rekindled their affair; but he insists that he has now broken it off for good, so he can marry Hermangarde. He sounds sincere — a sign that he doesn’t know Vellini (or himself) as well as he thinks.

To a contemporary audience, the story and setting immediately bring to mind Choderlos de Laclos’ frequently filmed “Dangerous Liaisons,” but to the characters — and presumably to the novel’s target audience — the similarities are deceptive. The Marquise explicitly defines herself as being of “the generation of Laclos,” which she contrasts to this newfangled 19th century.

This is both a boon and a drawback: Barbey d’Aurevilly, at least as presented by Breillat, is more realistic and matter-of-fact. By the same token, this robs the story of conventional resolution. There is none of the cosmic justice that triumphs at the end of “Dangerous Liaisons.” We are left up in the air, with a suggestion of more of the same.

A sense of realism is enhanced by the casting. While it’s hard to imagine finding Argento “ugly” (as Ryno calls her), one can see why he might consider her a crude “mutt” and then why he might become sexually obsessed with her. And Aattou, in his first film role, provides a natural freshness and a striking beauty; he is like a young Mick Jagger, but with softer, prettier features. At first he seems too young for the character; he seems — like Dorian Grey — resistant to aging, his features remaining untouched by his libertine behavior. When he and Argento have sex on screen, it’s genuinely sexy. Breillat has, for once, left violence and carnal disgust out of the equation.