Credit: Claire Folger/Focus Features

Amanda (Olivia Cooke) is a beautiful girl, but something’s off: she tries on smiles in the mirror like she’s flipping through makeup swatches at Sephora. Her therapist, she says, is still shopping for the right psychiatric term to explain her violent tendencies — she may or may not have murdered her own horse, among other misdeeds — and strange lack of affect, but Amanda already has a diagnosis: “I have a perfectly healthy brain. It just doesn’t contain feelings.”

Unsurprisingly, she also doesn’t have a lot of close friends; her old elementary-schoolmate Lily (Split‘s Anya-Taylor Joy) has to be paid under the table just to spend time with her. Soon, though, the two begin to reconnect, and find out how much they actually have in common: A love of old black-and-white movies, a disdain for the status quo, and a certain, shall we say, moral flexibility when it comes to solving problems like the aggravating presence of Lily’s wealthy, disapproving stepdad (Paul Sparks).

“Good breeding gone bad” is the tagline of writer-director Cory Finley’s acid satire, a sort of twisted millennial Heathers set in the stifling Land-Rovered luxury of suburban Connecticut, and it’s not hard to understand why these girls land where they do. Lily’s gilded lakeside home is a marble mausoleum, a place where fun goes to die; Sparks’ Mark is the kind of soulless Master of the Universe who keeps pictures of himself killing a lion and wielding a samurai sword in his office and wears full-body spandex to go for a bike ride; and her mother (Francie Swift) is barely there, a trembly, recessive Stepford wife.

With the pure-id Amanda, Lily finds a bracing freedom from all that. And Amanda, as apathetic as she claims to be, clearly longs for some kind of human connection. The idea of killing Mark comes on quickly, but things get murky fast; are they only bored and spitballing what-ifs, the homicidal equivalent of fantasy football, or could they really go through with it? Enter Tim (Anton Yelchin), a local drug dealer with big dreams that don’t quite match his brains or his rap sheet. He isn’t exactly an ideal assassin, but he does have a gun, and a plan begins to take shape.

This is the first film by Finley, a young playwright whose work has mostly only appeared on the far ends of Off-Broadway until now. Still, he writes and directs with the sure hand of someone who knows his milieu, pulling shrewdly layered performances from his two young leads and something much sweeter from the hapless Tim (though it’s mostly bittersweet now; Yelchin died only two weeks after shooting wrapped).

What begins as a gleefully nasty piece of work gradually picks up more nuance as it goes, adding dimensions to characters who could easily have coasted on the story’s arched-eyebrow burlesque. At just over 90 minutes, Thoroughbreds feels undeniably slight at times, even unfinished. But it’s also a fun, sharp shock of a movie; a poison dart with its own black little heart. B+

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