Musical theater and evangelical Christianity have traditionally been uneasy bedfellows, as one recent “American Idol” contestant learned to her peril. (She sang a song from “Jesus Christ Superstar,” with its mildly revisionist take on the Gospels, and was promptly given the hook by the voting public.) While composers are happy to send audiences out the door with a tambourine-shaking gospel number, they tend to shy away from the complexities of faith, let alone its more virulent manifestations. There’s a big difference between writing a song like “Sit Down, You’re Rocking the Boat” and actually rocking the boat with any talk of damnation.

This skittishness makes “Saved” one of the more tantalizing of recent film-to-stage projects. In adapting the 2004 indie comedy “Saved!” — by the way, when’s the last time a musical lost an exclamation point on its way to the stage? — composer Michael Friedman and co-librettists John Dempsey and Rinne Groff (all three teamed up on the lyrics) vacillate between trenchant explorations of evangelism and shopworn gags about “oral virginity” and the like. Even when these cheap shots tug the story into tamer waters, “Saved,” abetted by Gary Griffin’s unobtrusive direction and a splendid performance by Celia Keenan-Bolger, ultimately finds itself on the side of the angels.

Like another familiar story, “Saved” follows a good girl who finds herself in the family way. No virgin birth here, though: This Mary (Ms. Keenan-Bolger), a well-liked senior at American Eagle Christian High School, uses her barely existent feminine wiles in a failed attempt to “rescue” her platonic boyfriend, Dean (Aaron Tveit), from homosexuality. The duo’s transgressions earn her the enmity of much of the school, led by the conniving queen bee Hilary Faye (Mary Faber) and the heretofore sympathetic Pastor Skip (John Dossett), but gain her a sort of blasphemy chic among the school’s rowdier set, among them Hilary Faye’s wheelchair-bound brother, Roland (Curtis Holbrook), and Pastor Skip’s son, Patrick (Van Hughes), fresh from an eye-opening missionary stint in Africa.

The pairing of two mainstream musical-theater veterans — Mr. Dempsey co-wrote “The Witches of Eastwick,” while Mr. Griffin directed “The Color Purple” — with a pair of off-off-Broadway denizens could easily have spawned a calamitously lumpy mix of downtown attitude and middlebrow craftsmanship. But after a few rough early patches, the combination proves surprisingly felicitous. Ms. Groff and Mr. Friedman, who have previously anatomized loss via magic tricks (her “Orange Lemon Egg Canary”) and the childhood tropes of Etch-a-Sketch and hide-and-seek (his sublime score to “Gone Missing”), offer a welcome dose of emotional honesty to a story that balances mocking the American Eagle students’ prejudices and seeing the moral landscape through their Manichaean worldview.

The lyrics-by-committee approach has its ups and downs, as expected — you can decide for yourself which category the ‘Montessori’ / ‘whore-y’ rhyme falls into. And despite an array of melodies that evoke and often improve upon standard-issue Christian pop, Mr. Friedman falls into a few common adaptation traps. Chief among these is an insistence on having nearly every character voice his or her wishes and drives, regardless of whether this is necessary. Hilary Faye’s monomania receives a wry twist for a blissed-out toe-tapper called “Heaven,” which shows off Ms. Faber’s deceptively pleasing demeanor and offers a rare spotlight both for the winning Mr. Holbrook and for Sergio Trujillo’s inventive choreography. But the material for Mary’s overworked mother (Julia Murney, who does what she can), Pastor Skip, and especially the confused Dean has an obligatory feel. The movie rightly sensed that Dean’s significance to the story is over once he and Mary have sex; here, he not only gets a pair of songs to articulate his confusion but is spotlighted for an overreaching Act I finale.

With the exception of a predictable sequence in which two adults cite Scripture back and forth to plead their respective cases, the narrative perks up once Dean is sent off to a Christian “rehabilitation” facility and the focus shifts to Mary’s anguished choices. This isn’t the coy world of “Juno,” where teenagers agonize over whether their unborn child will end up in the hands of people with suitable taste in post-punk bands and horror movies. Mary agonizes over whether her unborn child will end up in hell:

Ev’ry day makes it harder
Ev’ry breath hurts me deeper
Ev’ry prayer screwed me over
Ev’ry choice took me farther from God

This is just one of several places where Ms. Keenan-Bolger is so guileless, so heartfelt, that she casts an even more unforgiving light on the show’s sophomoric moments. A sweet and charming junior high schooler in “The 25th Annual Putnam County Spelling Bee,” Ms. Keenan-Bolger has modulated her performance and crystalline soprano to capture the fears and hopes of adolescence with remarkable clarity. Whatever fate awaits “Saved” — it is a few minor cuts and tweaks away from being considerably better — she is the one truly essential component, a theatergoer’s answered prayer.

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