Stop me if you've heard this one. Julie Taymor, Lynn Ahrens, and Stephen Flaherty walk into a theater, and... Okay, forget it. It hasn't happened yet, but it should. Because the ability of Ahrens and Flaherty to evoke in their songs minutely specific times and places, and Taymor's gift for bringing specific visual and aural ideas to three-dimensional life, is a miracle waiting to happen.

Miracles, however, don't happen every day. You're constantly reminded of this while watching the show that trio should have constructed: Miracle Brothers, at the Vineyard. Written instead by Kirsten Childs, and directed by Tina Landau, the show mixes the story-theatre mysticism of Ahrens and Flaherty's Once on this Island with a visual sensibility that recalls Taymor's African-inspired artistry from The Lion King. The result is a show that will likely rank as not only one of the season's most volatile, but also the most pallid.

Their failure to bring to comprehensible life this bizarre folk tale is all the more unfortunate given what they manage to get right. When Miracle Brothers is at its best, it suggests a serious attempt to fashion a mythical tale that will relate universal truths about kinship and morality through a highly unusual lens; during the show's first few moments, for example, we're introduced to the Brazilian rain forest setting (the sumptuous work of G.W. Mercier) and a tribe of playful fresh-water dolphins in a smoothly cinematic sequence that suggests the panoramic openings of Disney's more ambitious animated films.

But just as it seems that being completely immersed in this foreign, yet strangely compelling, world is all but guaranteed, one of the dolphins says, in response to a description of a Brazilian's hair, "Did someone say kinky? Does that mean we're gonna have a lot of hot sex?". Any illusions of an evening of lush lyricism are instantly dispelled.

That line and many others like it are part of Childs's attempt to use contemporary vernacular to imbue the show with a sense of oral tradition. The effect, though, is jarring rather than jubilant, especially as we're meant to perceive the dolphins as magical creatures not only preternaturally observant, but capable of becoming other species during their nightly transformation rites. The dolphins' unique abilities seem less special when the creatures speak with so little poetry.

The problem is exacerbated when their transformation portal accidentally sends the dolphins-as-humans some 400 years into the past, to the 17th century. But the dolphins still use modern language that doesn't sit easily with the swarthy tale of betrayal and brotherhood in which they all become embroiled: Hearing slave owners, pirates, and high-born ladies communicate this way makes it difficult to the take the show seriously.

And Childs and Landau intend it to be taken seriously: The story about Fernando (Tyler Maynard) and Green Eyes (Clifton Oliver), two brothers who don't share the same skin color - their plantation-owning father sired one with his white wife and the other with a black slave - but try to maintain their relationship while combating prejudice from their own families and the outside world, is thought provoking. The brothers' negotiations of the barriers their outward differences have placed between them are intelligently addressed and presented, and the rift that gradually grows between them generates some legitimate tension as the first act comes to a close.

But for every song brilliantly conceived and executed, like "Tonight You Learn Capoeira" wherein Green Eyes teaches Fernando a secret dancing-based martial art (the angular, undulating choreography is by Mark Dendy), there's an "It's Really All Right With Me" giving a woman masquerading as a pirate (Anika Larsen) five minutes to spend spouting tired, vulgar masculine clichés. Spoken lines that highlight the spiritual connections between the brothers are rendered inert by exchanges like one in which a runaway slave girl (Nicole Leach) repeatedly says "I'm hot" and Fernando repeatedly and lustily replies "Damn."

Only Oliver, whose role is most lacking in such arrestingly anachronistic dialogue, realizes the full potential of his character: His yearning for freedom and acceptance compels his every word and action. He, Jay Goede (as the brothers' father Lascivio), and William Youmans (as the plantation's brutal overseer) are also the only ones who convince as 17th century Brazilians, and they stand in marked contrast to the thoroughly modern Maynard, the too-urban Cheryl Freeman (as Green Eyes's Spirit Mother), and the too-suburban Kerry Butler (as Fernando's mother).

Mercier's set, Anita Yavich's striking period costumes, Scott Zielinski's lights, and Jan Hartley's superbly understated projections make everyone onstage look good; orchestrator Daryl Waters, music director Fred Carl, and his guitar-and-percussion-heavy band make the music and the singers sound good. But only fleetingly, most notably in a stunning chase scene at the end of the first act, can Landau get all these elements to cohere into something exciting. Most of the time, the show feels like a half-completed jigsaw puzzle.

Childs's best writing always centers around the Capoeira rhythms and other traditional sounds; they make writing feel firmly evocative of the period, and seem as verdant as the tree-strewn set. Most of her lyrics and dialogue, however, haven't received quite the same care: That Miracle Brothers works at all is surprising enough; that it works as well as it does, in spite of its perhaps excessive ambition and clouded dramaturgical goals, is itself a miracle, if not yet one that fulfills more than a fraction of the promise that Childs and Landau suggest lies frolicking just beneath the surface.

Miracle Brothers
Through October 2
Running Time: 2 hours 15 minutes, with one intermission
Vineyard Theatre, 108 East 15th Street
Tickets online: Theatermania