The breath in “Breath, Boom” refers to the silent moment when fireworks are visible — before the boom catches up. For playwright Kia Corthron, the main question is whether Prix, an icy girl-gang leader in the Bronx, can ever escape the boom that chases after the fireworks from her handgun.

If you’re looking for a straight answer, don’t hold your breath. Although the Yale Repertory Theater’s posters advertise Breath, Boom as “an unflinching and ultimately hopeful portrait of urban desperation,” Corthron’s script is hardly that simple or optimistic.

The play, which ran off-Broadway last year, introduces Prix (Opal Alladin) in the mid-1980s as a stone-faced 16-year-old and episodically monitors her over the next 14 years. Prix’s growth reflects Corthron’s hopes for this neighborhood of urban, African-American poor. And the differences between Prix as an emotionally barren teenager worried about breaking parole and as a reticent 30-year-old checking in with her parole officer aren’t too inspiring.

Of course, that very well could be Corthron’s point. Flipping burgers at 30 is just the latest of a series life-draining experiences for Prix. (Previous siphons include the usual suspects: a sexually abusive father, a drug-addict and murderer for a mother, the apathy of society and the pregnancies of her gang sisters.) At least when Prix ran the neighborhood, her life had some purpose.

And that’s hardly the most troubling idea in Corthron’s play. More shocking is the assertion that gang membership is not just an alternative for African-American youth, but a rite of passage, a phase that only passes when a new generation has emerged to replace the aging “gangstas.” In fact, the Rep’s production, directed by Michael John Garces, feels more like a documentary — a slice of a terrible life — than a drama.

Granted, Corthron’s material isn’t original. There’s no new or surprising insight into the rough streets of the Bronx. But Corthron’s greatest gift as a playwright is her ability to write scenes that don’t seem stagey. And she’s able to turn a scene on one small detail — purposely buried toward the end of the dialogue — that can change the whole meaning of a scene or a perception of a character. That kind of confidence and competence is a treat to experience.

What seem out of place are the poetic elements, the metaphors and surreal moments that attempt to make Breath, Boom more than a sociological case study. No doubt Corthron needed some way to humanize her otherwise remorseless reality. The recurring motif of fireworks — Prix’s lifelong passion — is repetitive and heavy-handed. And the few forays into Prix’s mind that hint at some inner emotion, though powerfully staged, don’t help to elucidate how Prix can be, in the words of her 15-year-old cellmate, Cat, such “a cold fish.”

Still, Breath, Boom is far from a one-woman show. Alladin does a fine job as Prix, but the character, often standing still with a distant, chilling stare, isn’t too dynamic. Donna Duplantier, as the good-humored, spry Cat, with a miniature voice and contagious laugh, is a breath of fresh air amid the play’s opening scenes. Not only does Cat bring some cheer to the stage, but Duplantier, who played this role in the United States premiere last year, brings an acute sensitivity to her portrayal of Cat, allowing the girl to be silly and tragic simultaneously.

Set designer Wilson Chin and lighting designer Torkel Skjaerven provide realistic and shadowy acting spaces for this capable ensemble. There’s an empty lot with a chain-link fence, Prix’s bedroom and her prison cell — and all seem just right.

But neither these technical elements nor a booming hip-hop beat can keep up the show’s energy as it approaches the two-and-a-half-hour mark. Despite the fact that Prix describes her ideal fireworks display as one that never loses momentum, Corthron’s play outlasts its effectiveness in the concluding scenes. These last moments provide us an opportunity to ponder the next generation of gang members — those inside the womb of one of Prix’s former gang sisters, and the children of another, quarreling on the playground — but the ending also includes the first dramatic situations that don’t seem to ring true.

There are, finally, fireworks — Prix’s controlled chaos that’s awe-inspiring and beautiful. But like everything else in Breath, Boom, they’re also unsettling. As the colors blend together in the sky under Prix’s careful watch, it’s hard to forget the dream of suicide she described to Cat in juvenile hall — a great boom of fireworks, the violence bleeding with beauty. It’s also hard to determine if that dream has gone completely from Prix’s mind, or if it’s still hanging on for dear life.