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Irish writer-director John Carney’s Once, an intimate folk-rock musical, takes the brokenhearted ballads of the Frames frontman Glen Hansard as seriously as Hansard himself does—and that’s very seriously indeed. Wisely, however, Carney counters the bluster of Hansard’s choruses with a simple style and a humble tale: A scruffy Irish busker and girlish Czech pianist meet on the streets of Dublin and find they were made for each other musically, but perhaps not romantically. This may be the most naturalistic movie starring established pop musicians since Having a Wild Weekend, John Boorman’s 1965 Dave Clark Five anti-romp.

So strapped they can’t even afford names, the Guy (Hansard) and the Girl (Markéta Irglová) meet one evening after the busker has abandoned his wallet-opening Van Morrison covers for the originals he plays when the sidewalks are emptier. The almost annoyingly forthright Girl, who sells flowers on the street, asks who inspired one romantic lament, and the conversation then turns to vacuum cleaners. The Guy sometimes works in his father’s repair shop, and she has a busted Hoover. Cut to his singing, “You have broken me,” playing a guitar whose body he’s already strummed right through. That’s the movie’s most brazen song cue, and it’s a playfully ironic one.

Soon, the potential couple are having lunch, which Carney films from outside the cafe, as if he’s too much of a gentleman to come closer. They then adjourn to a music store where she demonstrates her chops and improvises a harmony for a song that begins, “I don’t know you/But I want you.” In a typical musical, that couplet would guarantee romance, but it turns out that the young-looking Girl—Irglová was 17 when the film was shot—has a husband and a young daughter. Her spouse is distant, both emotionally and geographically, leaving a climactic embrace a possibility. Yet the relationship in Once seems likely to be consummated in the studio, not the bedroom.

All of this—well, almost all—feels engagingly authentic. Carney is a former member of the Frames, and he knows this milieu. Both Irglová and Hansard, who collaborated on a 2006 album, are respectable nonprofessional actors. (Some 15 years ago, Hansard played the guitarist in The Commitments, a much rowdier Irish rock musical.) Although successful in their homeland, the Frames are still battling for an American audience, and Hansard is convincing as the hard-luck scuffler. With its natural-light cinematography and use of found locations, the film looks more like a documentary than a Hollywood musical; the bedraggled apartment building where the Girl lives with her daughter and mother, for example, clearly wasn’t created by the props department.

Though it can be appreciated as a canny piece of low-budget filmmaking, Once ultimately turns on the music. Viewers who thrill to these songs—not just the pretty parts where Hansard and Irglová harmonize but also the crescendos where the former thrashes and howls—should be beguiled. Those who wish the material took its tone more from the Girl and less from the Guy will be more skeptical. But then Carney is pretty skeptical himself. He’s made a star-is-perhaps-born fable that climaxes not when the musicians bewitch a mass audience but just when they manage to impress the demo-studio engineer. Such refreshing modesty recommends Once even to people who aren’t Frames fans.