At its root “Wild Rose” is a formula movie about a young singer with a dream, but it throws enough curves to keep it from falling into the cookie-cutter category. It also spotlights a star-making turn from Jessie Buckley in the title role.

When we first meet Rose-Lynn Harlan (Buckley), she’s just being released from jail after serving a stint on drug charges which, she’ll later claim, were a mistake. Wearing an ankle monitor under her high cowgirl boots, she saunters out jovially as guards and fellow prisoners cheer on her hope of success as a country-western singer. One might expect the sequence to be set in Texas or Arizona; the twist is that the locale is Glasgow, Scotland.

Rose-Lynn is not exactly a model. Her enthusiasm is obvious, but so is her recklessness. When she visits her long-time boyfriend Elliot (James Harkness), it doesn’t take them long to have sex in the park. And she’ll get into a fight when she goes back to her old haunt, the Grand Old Opry—Glasgow, hoping to perform there again.

Out of necessity, given her straitened circumstances, she shows up at the apartment of her mother Marion (Julie Walters), and tries to reconnect with her children Wynonna (Daisy Littlefield) and Lyle (Adam Mitchell), who are decidedly cool toward her. At her mother’s insistence she gets a job—as a housecleaner to Susannah (Sophie Okonedo), who’s astonished by the quality of her vocalism as she sings while doing the floors. (Director Tom Harper and Buckley stage the scene with infectious glee.)

Among other things, Susannah encourages Rose-Lynn to go to court to lift the restriction placed on her by her ankle monitor, specifying that she not leave her domicile at night. That limitation, her wary lawyer argues, prevents her from practicing her real profession as a singer, and, though the moment isn’t played in a triumphal way, the judge agrees.

Rose-Lynn then approaches Susannah, in her usual blunt way, about making it possible for her to fulfill her ultimate goal: to go to Nashville and become a luminary in the field she loves. Susannah demurs at funding the trip on her own, but devises a canny means of raising the money, and Rose-Lynn makes her way to the U.S., even though it means leaving her children behind at a particularly difficult moment.

In Tennessee, Rose-Lynn, as you might expect, visits the auditorium where the Opry performed for years, and she detaches herself from the tour to ascend the stage and begin singing. When other musicians join her, it appears that the film has reached its “Star Is Born” apogee, and you might think that its final act is preordained.

But in a final, satisfying twist, Rose-Lynn chooses another path, which one can read as redemptive in an unexpected way.

So the secret behind the success of “Wild Rose,” which easily have succumbed to the feel-good fantasy formula so familiar from past pictures, is, first, a script (by Nicole Taylor) that rejoices in upending expectations and direction that skirts the invitation to pander to the audience. The result is a movie that, despite a plot that is hardly innovative, is refreshingly unpredictable because it avoids hitting the normal narrative beats on the head.

None of it would work, however, without an outstanding performance at the center, and Buckley provides it. She sings strongly, and makes you believe that Rose-Lynn could really succeed in the music business. But while showing the character’s drive and talent, she is also unafraid to portray the woman warts and all; she is willing to show Rose-Lynn’s serious flaws, and to present her as unlikable in many respects, particularly in terms of her treatment of Wynnona and Lyle. Buckley, quite simply, makes Rose-Lynn credibly imperfect.

Happily, however, she does not have to carry the film entirely on her own. Walters, so good in comedy, demonstrates her dramatic chops here, while Littlefield and Mitchell aren’t typically adorable kids—Harper entices layered performances from them as well. And Okonedo makes Susannah supportive, but no pushover. The technical side of the film—Lucy Spink’s production design, Mark Eckersley’s editing, George Steel’s cinematography—is fine, but it’s the musical supervision of Jack Arnold that plays the largest role in putting everything across.

“Wild Rose” is definitely a crowd-pleaser, but one that doesn’t follow all the rules—just like its titular character.