The term folie a deux refers to two individuals who plan and commit crimes that neither would concoct on their own — the basis for (fact-based) movies like Hitchcock's Rope, or Peter Jackson's Heavenly Creatures.
To the canon add Cory Finley's creepy Thoroughbreds, the story of a prep school teen named Lily (Anya Taylor-Joy) who at the outset of the movie looks to be performing a good deed (the last you'll see in the film) — tutoring another senior (Olivia Cooke) who's been having trouble with her SATs.
We realize right away this ain't no after-school special. The opening images follow Amanda (Cooke) as she walks slowly through Lily's enormous, empty McMansion. The soundtrack hits us with the thumping, widely spaced beats of some massive orchestral drum. Finley is calling attention to opulence and emptiness of the scene, a nod toward what's to come.
The movie tonally has some hints of Michael Haneke or Yorgos Lanthimos, but Thoroughbreds has its own attitude and dark pulse, supplied by the chillingly good chemistry between Taylor-Joy and Cooke, the latter drawing us into her icy portrait of a budding sociopath who casually admits that she has no feelings. What she wants from Lily isn't instruction in mathematics, but in human emotion. She wants to know what Lily is feeling, how it guides her behavior.
As it happens, Lily is overflowing with emotions — most have to do with an intense dislike of her stepfather (Paul Sparks), who is roughly as nurturing as Amanda, and wants Lily out of his home and his life as soon as possible. The feeling is mutual.
It isn't long before the morality-free Amanda is suggesting that Lily consider how much simpler her life would be if stepdad weren't around — as coolly as if contemplating the next move on a board game. To underline the point, Finley has the two young woman moving pieces on stepdad's enormous outdoor chess board, an image that speaks to the movie's arch tone and the way it thickens its atmosphere of wealth and wickedness.
Lily isn't sure her friend is serious, but does nothing to dissuade Amanda as she pushes ahead with details just in case — enlisting (or perhaps coercing) the assistance of a local ne'er-do-well (the late Anton Yelchin, in one of his final roles), just in case they need a fall guy.
Is the plan real, or hypothetical? We saw the same mounting tension at work in Rope and Heavenly Creatures. Finley's movie, though, is only a folie a deux if you count human beings (or facsimiles thereof). There is a third entity involved — the smartphone, a device that promises engagement but promotes detachment.
This is sometimes pointedly funny. Amanda isn't sure she wants to go to college, and announces she wants to "Steve Jobs her way through life." At one point, Finley suggests that Amanda and her phone are equivalent — a lingering and carefully framed shot of Amanda lying motionless and e-motionless in her bed next to her iPhone invites comparison.
The human soul — is there an app for that?
Finley ends with a poetic epilogue that draws themes into focus, and gives voice to them. I'm not sure the movie fully earns it, but it does grab and hold your attention, thanks to the frighteningly good rapport between Taylor-Joy and Cooke.