There’s very little beauty in Beast. The feature debut of writer-director Michael Pearce, the film offers two characters with dark pasts and not much desire to change their ways. Moll is a young woman in a dead-end life, working as a tour guide and living with her parents so she can help take care of her Alzheimer’s-stricken father. Pascal is a loner whose fortuitous presence one morning saves Moll from the unwanted advances of another bad dude. “You’re wounded,” he says while looking at her hand, which earlier squeezed tightly around some glass. “I can fix that.” He’s referring to the literal gash, of course. But Pearce isn’t exactly subtle with this figurative sizing-up.

Moll (Jessie Buckley) is instantly smitten. Pascal (Johnny Flynn) is a poacher, fast driver, and hard drinker but seems to have nothing nefarious in mind when it comes to his new obsession. Still, her mother (Geraldine James, looking like a Redgrave) circles tightly; a serial killer is loose and had just abducted a teenage girl the night of Moll’s birthday BBQ, right before Pascal entered their lives. Though the impression is that Mum has always circled tightly anyway. She asks Moll to account for her whereabouts whenever she leaves the house and practically hisses when she accuses her daughter of lying, which is often. “You’ve come so far, Moll,” she cryptically says.

Moll and Pascal take to each other quickly, so when he becomes a person of interest in the serial killer case, investigators talk to her, too. She provides him an alibi for the latest disappearance and doesn’t entirely believe that the guy she’s been having an “amazing” time with could be a murderer. But there’s always a little doubt.

Beast is a grim fairy tale. There are hints that Moll is not quite human: that long hair that pops out of her neck, for example, or her claiming that what she loves about Pascal is “his smell.” (Later, she tells someone she can’t stand that she’s always hated his smell.) When the couple are going at it, you hear barely there growls underneath their kisses. Because Pascal is wild, too. They’re both quick to vicious anger. But Moll is the more vulnerable one, often dreaming of being attacked and offering her condolences to the mother of the murdered, even though she and seemingly the rest of those gathered at a service vehemently want Moll to leave.

As the story wears on, Buckley’s performance becomes more remarkable. It’s a raw, animalistic turn; she plays Moll like a woman with all her nerves exposed. Her character must fend off the town’s bile, and she’s not above flat-out roaring at those who try to chase her out. Flynn is serviceable as the dangerous stranger, but Buckley is the one you’ll watch.

Beast’s tone is uneasy throughout, from its opening scene of a search party and impromptu memorials to Moll’s interrogation by a creepy investigator in a dim room to its bloody close. You’ll cringe as Moll does things such as lying down in a victim’s former shallow grave or closing her fingers around that glass. The sense of jeopardy is palpable. But the film’s more impressive achievement is a third act that feels like a natural progression as well as a twist that isn’t a complete cheat. Pearce doesn’t always take the more difficult route—there are enough cheap jumps to make you think you’re watching a horror movie. But overall, Beast succeeds because of his instinct.

Beast opens Friday at Landmark E Street Cinema, Landmark Bethesda Row Cinema, and Angelika Film Center Mosaic.