Unbeknownst to Rick, the track, a love song, is a phenomenon, with millions of streams. It becomes a No. 1 hit, and everyone—including Aja and Rachel—is crooning along to it everywhere. Rick is, in effect, secretly a world-famous songwriter, and, though he’s happy that Danny has managed to reinvent himself, he is resentful that he hasn’t got the acclaim, the money, or the career that writing a hit song should bring. There’s no paper trail to show that the song is his, and no proof that Danny ever heard him play it. What’s more, Rick can’t get through to Danny, because the pop star’s brash and aggressive manager (Jack Reynor) refuses to put Rick through, and responds to his claims with threats. Direct action is required: Rick and his bandmate and best friend, Sandy (Peter McDonald), head to Los Angeles to confront Danny in person.

Rudd’s natural air of genial tension, of neurosis without an edge, plays into his character’s rigidly disciplined but relentlessly upbeat domesticity. Rick is tightly scheduled, punctilious to a fault, endowed with verbal wit that gently but firmly shapes and smooths social interactions. Warm and wise with Aja, and never nonplussed when she out-cools him or simply fails to flatter, he also performs middle-aged hotness just self-deprecatingly enough. His charming but locked-in sense of commitment makes him an apt front man of the Bride and Groove—he glows with a little more wattage than his bandmates do—but it’s also why he’s not the group’s real leader. That would be the drummer, Binzer (Rory Keenan), who sits at the back of the stage, surveys the group and the roomful of revellers, and pliably makes adjustments that keep the party going. Rick’s taut precision, by contrast, can cause trouble at the mike; when Danny first asks to join in on a song or two, Rick—fiercely protective of the band’s routine and his place in it—refuses, until Binzer firmly implores him to be a sport. There are roots to Rick’s extreme defensiveness. The American band that he’d been part of in his youth, called Octagon, had been big enough to sign with a record label, but when Aja was born Rick took a year off and the label dropped him. He’s been fortunate enough to make a living as a musician, but his bitterness about the loss of that big break lingers.

When Danny performs, though, something startling is revealed, something that’s built into the casting. Rudd just sings, but Jonas is a singer: Rick delivers songs, whereas Danny makes them his own. Performing “I Wish,” Danny approaches melody, rhythm, and lyrics with a sense of freedom that transcends the sheet music and gives the composition a three-dimensional life. What Danny does, Rick can’t. Their respective performances mark the difference between a mere professional and a star, with one caveat: if not for Rick, Danny would have no new song to infuse with life. Danny’s gift is what he does onstage; Rick’s is what he does sitting alone in a room.

Unfortunately, the movie doesn’t follow through on this idea, and Rick’s hidden aptitude remains largely invisible. When he sings his own song at the wedding in the opening scene, a bandmate reproaches him, implying that Rick has tried out his own material before with similarly dismaying results. (The bandmate tells him to sing only “the hits” and reminds him that their job is basically to be “human jukeboxes.”) The setup is too pat. In Rick’s many years as a wedding singer, has he never won any admiration for his songs? Not even at home? Has he kept going with no positive reinforcement at all, based on nothing but his own confidence in his talent? The film’s themes of creative frustration and unmet potential are fruitful and fascinating but are left undeveloped, and the movie is painfully short on psychology. What takes its place is feel-good human connection and reconciliation, whether found in unlikely places—such as in a climactic showdown between Rick and Danny in Los Angeles—or in its familiar setting, at home.

Sentimentality has been a consistent strain in Carney’s directorial career. He won international recognition for the 2007 romantic musical drama “Once,” set in Dublin, about an encounter between an Irish and a Czech musician. His 2013 drama, “Begin Again”—which he’d originally titled “Can a Song Save Your Life?”—is the story of a man who loses his job as a record executive but gets his musical mojo back when he connects with a young woman singer-songwriter. In those films, as in “Power Ballad,” music serves not to undo and reshuffle romantic relationships but to restore and reinforce them, even as it forges new emotional bonds. Carney is a moralist, a filmmaker of fidelity—and of renunciation, depicting the romantic near-misses and what-ifs that his characters leave behind.

In “Power Ballad,” Carney’s musical moralism remains superficial, worked out neither in the detailing of his characters nor in his pragmatic, efficient direction. Rick’s unyielding faith in his own artistic powers is a weighty secret and a constant burden; his absence of torment in the face of it, his apparently content and unruffled life with his friends and family, ultimately suggests less about Rick’s temperament (which gets an all too scant workout) than about Carney’s own mild-mannered aversion to such inner conflicts. The story’s most powerful and expressive possibilities go unexplored, in a way that reflects the substance of the movie itself: just as “Power Ballad” emphasizes the difference between a songwriter and a singer—between the creation of formidable raw material and the amply imaginative realization of it—it also unwittingly displays the distinction between screenwriting and directing, between potent ideas and their bland development. The movie is more than a celebration of persistence in the face of rejection, of faith in oneself, or of the power of love. It exalts, above all, the practical genius in the division of labor. ♦