Amanda (Olivia Cooke) has... emotional issues. In that she doesn't have any emotions. With a troubling incident connected with horses in her recent past (she does have a fixation on horses, for better or worse) that has resulted in her struggling at school, she is ordered by her mother to go along to the Connecticut mansion house of Lily (Anya Taylor-Joy), who used to be a friend when they were very young, but they grew apart. Lily is trying to be nice to Amanda and help her with her studies, but Amanda makes it clear she knows why she has been accepted into her old acquaintance's home: Lily was paid by her mother. This creates an understandable chill between them, but Lily has her problems too...
You can tell Thoroughbreds began life as a stage play, as it has the leaning towards a chamber piece that really could have taken place in the same location, the mansion or even a room contained within, despite how its writer and director Cory Finley opened it out to an extent to take in the surroundings of the two girls' relationship. At first we think Amanda is going to lead the ostensibly pure of heart Lily astray, but as the story progressed it was plain to see there was more to it than that, and they were having a bad influence over one another in turn as Lily struggles with the stepfather she initially cannot admit she hates, but later owns up to precisely those feelings.
The shadow of Peter Jackson's cult classic Heavenly Creatures was cast over Finley's screenplay, another tale of two young souls whose union brings them to an act of horrendous violence, but that was a true story, and Finley here did not have to stick to any facts and could toy with the characters - and the audience - as he saw fit. If anything, the New Zealand film had at least the saving grace of us being well aware the friendship, the love even, at the centre of the drama was sincere, but with this you were constantly unsure of who was doing their best to manipulate the other, and whether either genuinely had a grasp of what they were proposing, with all the accompanying implications.
Cooke and Taylor-Joy were very well photographed by Lyle Vincent, so that we would be distracted by their surface beauty before realising their hearts were dark as pitch, and that contrast between outward attractiveness and inner corruption went a long way to keeping us watching, even if it also left the concluding scenes more predictable than you imagine was the intention. Even so, the ultimate betrayal which neither regard in those terms made for an uneasy sense of injustice, as if both believed the other deserved what came to them, while not able to conceive of how they had got one of the most supposedly simple connections in life, the friendship of someone your own age, with your own interests, from the same area, so disastrously wrong in a manner inevitable but no less unfair.
Yet of course, friendship at any age can be fraught with difficulty, and the fragility of such an arrangement is not often acknowledged in the movies where "friends to the end" plots prevail to reassure the audience who don't wish to know that this person they have allowed into their lives, have shared so much with and have you convinced your bond is true, could turn against you so dramatically. There are plenty of reasons such things can go wrong, from personality flaws to circumstances changing to goodwill souring to resentment when expectations are let down or simply because a scapegoat is needed and one friend is at hand to fulfil that role, however reluctantly, but Finley knew to see this played out between two young girls so full of promise had a worrying power all its own. Needless to say, that worked against any humour here, but if you wanted to see two keen young talents get their teeth into a couple of strong roles, then as grim drama it hit its target. Anton Yelchin, in one of his final films, matched them, going from sleazy to unexpectedly sympathetic in a way denied the leads, purposefully. Music by Erik Friedlander.