They sneak up from the shadows, sniffling and giggling. The singing pigs that lurk and shimmer through “The Butcher Boy,” which opened at the Irish Repertory Theater on Monday, are silly but also half-threatening. Below the neck, they’re dressed like city dwellers in 1960s Ireland, where the new musical, written and composed by Asher Muldoon, is set. From the jowls, however, their muzzle masks are oddly emotionless.

The chorus of pigs seems like a totem of indecency, embodying the dark, unknown depths of the show’s narrator, Francie (Nicholas Barasch), a playful boy with fire-colored hair and a relentlessly sunny disposition. In her upbeat brogue, Francie tells a story of childhood misdeeds and alienation with a zeal that belies what appears to be the threat of violence promised. If there’s danger beneath her sparkling smile, Francie may be a little too good at hiding the knife.

Based on Patrick McCabe’s 1992 novel, “The Butcher Boy” presents a myopic take on a troubled upbringing – call it an anti-aging tale. Francie claims her teenage years were idyllic, though scenes from the musical clearly prove otherwise. He and his best friend (Christian Strange) fish, party and steal comic books from a nerdy classmate (Daniel Marconi), whose mother (Michele Ragusa) fatally mocks Francie and her parents based on social class, calling them pigs.

“It was a sweet, simple moment,” Francie sings as her dad (Scott Stangland) belts him around his butt. “We were happy,” he says before coming across his mother (Andrea Lynn Green) about to hang herself on a fuse wire. The motor-mouthed Francie turns to the public with asides and diversions that conceal as much as they reveal.

In the novel, McCabe’s prose is propulsive and unpredictable, bordering on the stream of consciousness and bubbling with proto-punk sensibility, much like Irvine Welsh’s “Trainspotting,” published in Scotland a year later.

But putting a narrator as unreliable as Francie at the helm of a musical is tricky business. Should an audience believe what they hear or what they see? It depends on which is more compelling, and the results here are hard to decipher. Is Francie only fooling himself or is he trying to fool everyone? The answer often seems to be both, and it’s a tricky deception for a performer to pull off, especially when narrating and participating in two and a half hours of action.

“The Butcher Boy” could have been turned into a sharper, more powerful black comedy if the score of Muldoon, who is not yet a senior in college, had developed a more distinctive point of view. His conscientious touring through Broadway-style pop, vaudeville and Irish influences is largely referential.

The production, directed by Ciaran O’Reilly, uses graphic shorthand to suggest the tension between Francie’s island spirit and the outside world. The slatted wood walls of Charlie Corcoran’s set resemble a treehouse, while an oversized rendering of a rotary TV serves as a backdrop for Dan Scully’s projections. The screen dominates the compact scene, giving a brief nod to the hustle and bustle of the 1960s and Francie’s fondness for “The Twilight Zone,” but the importance of mass media to Francie’s tortured descent is either overestimated or underestimated.

“The Butcher Boy” centers Francie’s perspective on a fault, so that other characters’ beliefs are mediated by her own. It’s a powerful concept but requires tricky physics that directing a three-dimensional story tends to challenge. When characters who have no emotional agency express themselves in song, whose heart can they claim to touch? Francie seems determined to prove that he has none himself.

There are promising moments of touching feeling at the end of Muldoon’s score, in ballads that seem to offer an unlikely resolution, before Francie prevails with yet undetermined rage. But by the time Francie’s own mask finally falls, the revelation seems eerily bloodless.

the butcher boy
Through 9/11 at the Irish Repertory Theatre, Manhattan; irishrep.org. Duration: 2h30.