Near the end of the first act of “Leap of Faith,” the new Broadway-bound musical that opened Sunday at the Ahmanson, Nicholas Barasch, as the young boy Boyd, movingly sings “Walk Into the Sunset.” Crippled after a tragic accident, Boyd prays for a miracle. If his angelic voice can’t pierce the heavens, nothing can.

It’s a small moment, but it redeems — spiritually and otherwise — this big-name, big-budget musical about the power of faith.

Up until that point, “Leap of Faith” fails to make any impression. The plot, like the dancing, shlumps forward in feet-dragging fashion. The characters — single mom, sleazy con-man with a conscience, feisty kid sister, big black woman — might as well be cardboard cutouts. The dialogue exhausts every cliché in the book. The songs don’t catch.

But of course, sometimes it pays to have a little faith.

When Barasch opens his mouth, there is a sudden, collective intake of breath. Something awakens — a spirit, maybe — that guides the rest of “Leap of Faith” to its predictable, impossible, soaring conclusion.

It’s really no surprise that it takes the special innocence of a child in song to give this oversized musical its humanity. The other actors grab hold of it and, for the most part, keep it alive for the rest of the show.

It’s about time those other actors get mentioned, specifically Raúl Esparza as phony faith healer Jonas Nightingale and Brooke Shields as small-town-mom-in-crisis Marva McGowan.

Marva spends her days waitressing at a small café in rain-starved Sweetwater, Kansas. We already know Marva’s story — vibrant youth undone by personal tragedy. Now, all she’s got is her son, Boyd.

Jonas is a traveling salesman of sorts, except he traffics in religious awakenings. He and his gospel choir travel from town to town swindling people out of their hard-earned money in exchange for easy-earned salvation. They get stranded in Sweetwater when their bus breaks down.

Crises of conscience ensue, and people’s faiths are tested. Love happens. The sheriff, angry that the unemployed townsfolk are giving money to Jonas rather than donating to the water cause, tries to run the tent show out of town.

All told, the script doesn't offer much in the way of surprises.

Esparza, a Tony-nominated Broadway veteran, is a transcendent vocalist and good at playing a sleazeball. He really lights up in the second act, which is better all around than the slow-moving first. “Jonas’ Soliloquy” nearly steals the night.

But what about Shields? There is this compulsion, in casting big shows, to get big stars. Shields, stunning as ever, may not be the best possible person for this role, but she does not disappoint either. Of course, she’s no match for powerhouse vocalists like Esparza or Kecia Lewis-Evans, who plays Jonas’ choir director Ida Mae Sturdevant. But she’s a fine actress, capable of imbuing her soft and sultry voice with nuance. And she and Esparza generate a nice chemistry.

Alan Menken’s (“The Little Mermaid,” “Beauty and the Beast”) gospel-influenced score (Glenn Slater did the cliché-ridden lyrics) doesn’t do Shields any favors; it’s big and over-the-top. “Step Into the Light,” the diva-licious “Are You on the Bus?” and the crowd-pleasing finale song “Leap of Faith” live up to Menken’s potential, but his finer days are behind him. Where are the memorable hooks?

Rob Ashford’s direction is clean, as is Robin Wagner’s scenic design. Sweetwater is rendered in various shades of sunset that overlook a field of corn. Donald Holder shrinks and expands his spotlights to great effect.

But what’s with Ashford’s choreography? The ballet sequences aren’t offensive, but they serve no clear purpose other than to transition between scenes. Their elimination would be a good start to cleaning up the first act. Another problem is the ending, which earns tears but is impossible to pull off seriously. It will take a lot more than faith to get this show to Broadway.

Still, there is something undeniably irresistible about “Leap of Faith.” The musical pulls out every sentimentality in the book, but that eventually stops mattering. By the end, there is a sense of perfect contentment, if not spiritual fulfillment.

Maybe there is such a thing as a miracle.

Reach Senior Arts Editor Jason Kehe here.

For 2012 Tony Awards coverage, click here.