You can almost hear the stage creaking beneath the action of Cory Finley’s screen adaptation what was originally conceived as a two-character play. He’s expanded “Thoroughbreds” and transferred it to real-world settings, of course, but the theatricality of the plot and artificiality of the dialogue—as well as the affected nature of the performances—still smell of the boards. References to plays like “Equus” make the feel all the more obvious.

That’s not fatal to the movie, of course. Plenty of plays have survived the transition to film, even with less of an effort to “open them up.” The difference is that they were better plays than this very black comedy.

The main characters here are, in effect, two “bad seeds.” Lily (Anya Taylor-Joy) is a rich, smart, apparently cool but clearly troubled girl, who—we learn—have been suspended from her posh prep school and is anxious to be readmitted. She despises her controlling stepfather Mark (Paul Sparks) and has little love for her mother (Francie Swift), who, it appears, will go along with his suggestion that they send her off to a school for girls with behavioral issues.

Lily is being visited by her childhood friend Amanda (Olivia Cooke), ostensibly for help in preparing for her exams, but actually to provide some much-needed companionship. Amanda is an outcast as well, and a far more frazzled, unkempt one, though she admits to feeling nothing about anything—including her killing of a horse.

The two spar verbally for a considerable time, until they settle on a joint project: killing Mark, whose constant work on an exercise machine upstairs sends a throbbing noise throughout the place—a sign of his pervasive, and unwelcome, influence.

Eventually the two girls decide to lure small-time drug-dealer Tim (Anton Yelchin), who’s already on the books as a sex offender, into actually doing the deed. Even he proves unwilling to get involved, though, so the duo will have to take care of it themselves. In the end, however, one proves definitely the dominant force, and which one that is, and how she contrives to escape responsibility, provide the matter of the luridly twisted conclusion.

Finley is clearly adept at penning sharp, bitchy dialogue, and at contriving a sly tit-for-tat sort of structure that mimics the work of, say, the Anthony Shaffer of “Sleuth.” His touch is not as sure, though: the entire subplot with Tim seems a random digression. Even though it’s good to have the opportunity to watch, in what was probably his final role, Yelchin—a fine young actor taken from us far too soon—the episode drains tension from the narrative, which is why the final reel has a flaccid feel to it despite its supposedly revelatory and shocking quality.

One does have to notice the expertise with which cinematographer Lyle Vincent lays out the scenes in carefully-composed widescreen images, and the sound design which, along with Erik Friedlander’s brooding score, contributes to building an oppressive atmosphere.

On the other hand, there is an (admittedly intentional) artificiality to the lead performances that is more likely to engender respect rather than any emotional response. Taylor-Joy and Cooke go through the hoops (or perhaps more appropriately, jump the hurdles) that Finley has set out for them, so to speak, but they can’t bring any human genuineness to characters that are all affectation. They speak their lines with appropriate degrees of archness and the swiftness or deliberation required in the particular moment, but never are any more credible than the verbal sparring partners in “Sleuth.”

Of course like that play, “Thoroughbreds” is an entirely artificial construct designed to please through a satisfying puzzle-like maze of words and incident. One can imagine it working better on stage, where its self-conscious cleverness would be more at home. On the screen, its synthetic character and mannered style are more likely to frustrate than captivate.