There is nothing more enjoyable than a film that shatters your expectations, turning a confident hunch about what’s coming next into smithereens of doubt. The British thriller “Beast” does it strikingly well. Michael Pearce’s accomplished debut film slowly and remorselessly turns a rural story of young love into an emotionally charged murder mystery from a feminine perspective.

The story is set on a small island on the English Channel. It’s a tight little postage stamp of a place where people might not know every individual detail about one another’s lives, but they know enough to form strong opinions.

It’s not the best place for an independent-minded young woman who is ready to rebel unless she’s prepared to slash through obstacles with little concern for the consequences. That turns out to be the case with Moll, a wallflower still living with her commandeering mother (played with iron willpower by Geraldine James). She dutifully follows her mother’s restrictive orders, wears childish pastels, sings in the church choir and rejects the attention she receives from the isle’s limited range of suitors.

Why Moll is so inscrutably reserved is revealed in a gripping performance by mesmerizing newcomer Jessie Buckley. The film is not so much a psychological thriller as a performance-driven portrait of a vulnerable-yet-ferocious woman in a very dangerous predicament, and the electrically intense Buckley is the actress to carry it.

The action opens at a large, boring birthday party in Moll’s honor where she walks off to spend the night dancing and drinking. Mother reminds her that “there’s a killer stalking this island.” In the past four years three girls were kidnapped and found in shallow graves, and a fourth remains missing. (The story is inspired by a real series of attacks in the 1960s.)

The case becomes Moll’s central concern when she is rescued from the crude advances of a pushy bloke. Her knight in armor, Pascal (Johnny Flynn), is a person of interest in the ongoing police investigation.

Moll finds the handsome brute’s take-control attitude enthralling. They seem like a match made in — well, purgatory at least. He is rough and crude and smelly as the outdoors but has fragments of sensitivity that the well-scrubbed lumps in the island’s small dating pool lack. With her flaming red hair and his blond locks all tangled in Titian curls, the matching misfits look made for each other. Moll and her new love become a new age Bonnie and Clyde. After her first romp with Pascal in the outdoors, Moll brings the dirt home on her clothes, drops onto her mother’s immaculate white couch, and spreads her legs apart like a man filthy after a day of horseback riding. It’s a pose of psychosexual victory.

This is not an inspirational drama about finding yourself. It’s a gothic thriller with steadily increasing tension and violence, whose heroine grows darker as she goes deeper into moonlight and surreal dream sequences. “Beast” announces an original creative sensibility and reminds us how much cinema is improved when that attitude is allowed to follow its own path.