Glen Hansard and Markéta Irglová's story could be a movie of its own.

Cult rocker, passionate but perpetually unlucky in love, meets preternaturally wise girl half his age, finds romantic and artistic fulfillment. But after February's fairy-tale Oscar win for best song on the

Once

soundtrack, Hansard and Irglová faced the challenge of linking their current success to their musical past, particularly to Hansard's 18 years as the frontman of Irish band the Frames.

For Tuesday's show at the Tower Theater, Hansard and Irglová billed themselves as the Swell Season, after the title of their 2006 album, but their four-piece backing band looked suspiciously like the Frames, whose half-dozen albums were, unlike the

Once

soundtrack, for sale in the lobby.

The volume level rose slowly but steadily through the course of the two-hour show, from "Say It to Me Now," which Hansard sang unamplified at the edge of the stage, to the storming encore duo of "Fitzcarraldo" and "Star Star," which have long been highlights of the Frames' live set.

With her delicate piano and breathy voice, Irglová was the earth to Hansard's fire. When they harmonized on the plangent "Falling Slowly," their Oscar-winning song, her voice soared above his, a wisp of cloud atop his jagged vocal peaks. Irglová's calming presence softens some of Hansard's quintessentially Irish bent for anguished theatrics, which at their most extreme approach a kind of sensitive machismo.

It wasn't so long ago that Hansard and Irglová were playing the 100-seat Tin Angel, but the Tower Show capped a monthlong tour in front of the largest American audiences of their career. Although Hansard dismissed his newfound celebrity in unprintable fashion, he marveled at their undreamt-of stardom, which he likened to kicking a ball that flies into the air and over the horizon.

"Ninety-nine percent of you is amazed how far the ball went," he said. "And it totally overshadows the one percent that says, 'I want my ball back.' "

The Irish band Interference, whose singer, Fergus O'Farrell, Hansard has cited as a formative influence, opened the show and returned during the encores to play "Gold," whose inclusion on the

Once

soundtrack brought them out of years of obscurity and near-retirement. With his elastic phrasing and swooping high notes, O'Farrell presided over an eight-piece lineup whose fanciful, folk-tinged arrangements followed every curve.

In "American Townland," O'Farrell's lyrics approached bombast. But elsewhere, he balanced ardent declarations of love with sudden turns of phrase whose opaque beauty brought the room to a hush.