Lily (Anya Taylor-Joy) is in a bad place.  She’s in trouble with her posh boarding school, and stuck at home between semesters with her well-meaning but uninvolved mother and douchebag-extraordinaire stepfather, Mark (Paul Sparks).  He and Lily live together in hostile tension, both affecting a façade of chilly politeness that barely conceals their mutual hatred for one another.  Meanwhile, the mother of Lily’s middle school classmate Amanda pays her to tutor her daughter, itself a transparent excuse to provide Amanda with some social contact.  Amanda has become an outcast after brutally killing her family’s crippled horse, which in her mind was an act of mercy.

When the two reconnect, Lily initially does her best to be gregarious and proper, but Amanda has none of it.  She freely admits to Lily that she has no feelings whatsoever, and hasn’t for as long as she can remember.  Lily is doubtful first, but soon sees that Amanda is the real deal, and finds herself drawn to her refreshing lack of dishonesty and judgment.  When Amanda casually proposes killing Mark, Lily is horrified – but tempted.

Thoroughbreds is insidious in the best way.  Its hyper-intimate setup, consisting of a tiny central cast and even fewer settings, makes it easy to get lost in.  This spatial confinement, along with a liberal use of wide-angle lenses and a cold, desaturated palate, creates a palpable sense of place; immersing us in the uninviting emptiness of Mark’s mansion, the movie’s primary setting.  If you haven’t guessed already, Thoroughbreds is a very talky movie, which is only to its benefit.  The dialogue is so good that the scenes of Lily and Amanda making conversation, which make up the lion’s share of the movie, aren’t just watchable – they’re downright compelling.

This is also due in no small part to the dual lead performances of Anya Taylor-Joy and, especially, Olivia Cooke, which form the bloodless heart of the movie.  The latter’s Amanda is a force to be reckoned with; she’s dead-eyed, sociopathic, and often hilarious.  Taylor-Joy, for her part, gives us an initially sympathetic protagonist who seamlessly morphs into something more sinister over the course of the movie.  Anton Yelchin also shows up a ways into the story as a small-time drug dealer whom the two girls rope into their not-so-hypothetical murder plot, providing some much-needed low-class contrast to the girls’ affluent and sheltered world.

At a meatier length, Thoroughbreds’s brand of dark wit, as clever as it is, would grow tiring, but the movie wisely stays as lean as its two leads, remaining laser-focused on the plot and ending precisely when it’s resolved.  The final fifteen minutes aren’t quite as gripping as the rest of the movie, but writer/director Cory Finley still ends things on a perfectly satisfying note.  Thanks to its stellar cast and razor-sharp writing, Thoroughbreds is a deliciously twisted black comedy, one that has “future cult classic” written all over it.