Here is a psychological suspense thriller and an anhedonic daymare: absorbing, if finally anticlimactic. It is Bret Easton Ellis out of Patricia Highsmith, and there’s also an interesting touch of Lady Macbeth’s murderous MO.

Olivia Cooke plays Amanda, a disturbed wealthy teenager, just out of a psychiatric facility for something horrible she did to her mother’s thoroughbred horse. Now she is being sent for a bizarre remedial “playdate” or home-study session with the equally privileged princess who lives in the same chi-chi neighbourhood and with whom Amanda has had a brittle acquaintance since childhood. This is the eerily groomed and detached Lily, played by Anya Taylor-Joy.

After an initial froideur, their relationship blossoms once more and they become deadpan-dysfunctional besties, hanging out, affectlessly watching TV, bonding over a shared loathing of Mark (Paul Sparks), Lily’s asshole of a stepdad, who is threatening to send Lily away to a special school. Pretty soon the girls are wondering out loud if it would be such a bad thing if Mark were to be killed and if they might employ the local drug dealer, twentysomething Tim, who creepily hangs around their school-age parties – sadly, the final performance from the late Anton Yelchin.

First-time writer-director Cory Finley very cleverly creates the airless, loveless world of emotional aridity and extreme wealth in Lily’s clenched household, the manicured lawns and the spotless hotel-lobby-like rooms – including Mark’s gruesome alpha-male den with its classical figures and photograph of Mark himself solemnly posing with a samurai sword.

It is initially gripping, with agreeably chilly Hitchcockian echoes, although the plot is a little less satisfying when it comes to the way the horrible murder plan itself appears to go wrong. Cooke and Taylor-Joy are convincing in their ruthlessness: Stepford sisters in the cause of self-gratification.