Joséphine Japy, left, plays Charlie, a teen with a girl-crush on a new classmate, Sarah (Lou de Laâge), who holds a family secret. (Film Movement)

Breathe,” a French drama of teenage psychopathology in the extreme, is like “Mean Girls” remade as a thriller. Impeccably rendered by Joséphine Japy and Lou de Laâge as the adolescent heroine Charlie and her high school tormentor Sarah, the friendship at the heart of this fine but hard-to-watch film is a wormy heap of decay.

Director and co-writer Mélanie Laurent — an actress who is here making her second foray as a feature filmmaker — shows both a keen eye for visual style and a sensitive hand with actors. If the story, inspired by Anne-Sophie Bras­me’s novel, borders on the luridly pulpy, its central performances are quiet tours de force.

Mousy, asthmatic and still a virgin, 17-year-old Charlie develops something of a girl-crush on Sarah almost from the moment that she lays eyes on her new classmate, a worldly, flirtatious bad girl with an ever-present cigarette dangling from her full, laughing lips. But after these two almost instantaneous BFFs return from a brief vacation to the countryside with Charlie’s mother (Isabelle Carré) — during which Sarah shows herself to be strangely touchy, cruel and mercurial — the hairline fractures in their short relationship deepen, opening the way to a psychic rift that threatens to become something far more seismic. Sarah’s behavior quickly goes beyond catty, in ways that will at first seem inexplicable (even for those who are well versed in the ways of teenage girls).

That this casual viciousness with Charlie turns out to be based on a secret familial dysfunction that Sarah has somehow managed to hide from the world doesn’t let her off the hook. She’s a monster through no fault of her own, the film suggests, yet it’s almost impossible to feel sorry for her.

It’s also hard to know exactly what else “Breathe” wants us to feel or think, especially when Charlie, with whom our sympathies lie, goes off the deep end. In some ways it plays like a horror movie, in other ways it’s almost a documentary.

The most interesting thing about the movie is the balance of tone that Laurent strikes between recognition and repulsion. In “Breathe,” Sarah is both a miscreant and every teenage girl you’ve ever met.

Unrated. At the Angelika Pop-Up at Union Market. Contains obscenity, teenage smoking, drinking and drug use, and brief violence. In French with subtitles. 91 minutes.