Convinced she was doing God's work by sleeping with her fey ice-skater boyfriend to keep him from "turning gay," blissfully naive and blindly devotional Mary (Jena Malone) is now a knocked-up senior at American Eagle Christian Academy -- and suddenly having dark-comedy doubts about everything she's been taught to believe.

This is the foundation of "Saved!," an incisively wry, low-key indie that almost -- almost -- manages to deliver its sardonically tart message of tolerance without making one-dimensional cartoons out of its judgmental, Bible-beating antagonists.

Co-written and directed by first-time filmmaker Brian Dannelly (who attended a Catholic elementary school, a Jewish summer camp and a Baptist high school while growing up), "Saved!" is narrated from Mary's point of view as she navigates a snake pit of high school gossip dangerously coupled with religious self-righteousness.

She begins the school year on top of the social heap as the best friend of dulcetly domineering prayer-leader Hilary Faye, played by recovering pop princess Mandy Moore with an evangelical earnestness that veils the actress's sly, winking hint of satirical self-awareness. "I'm saving myself until marriage," she scowls with virginal determination while squeezing off shots at a Republican gun range, "and I'm prepared to use violence."

But then Mary misses her period, which she thinks could mean either cancer or pregnancy ("Please let it be cancer! Please let it be cancer!") and her boyfriend gets packed off to a "Christian treatment facility" (where he meets more cute boys with his "problem").

A crisis of faith sets in as she knows she'll have to hide her condition from everyone in her life, including her mother (Mary-Louise Parker) and the school's benignly un-hip pastor-principal (Martin Donovan), who begins school rallies by whooping, "Let's get our Christ on! Who's down with the G-O-D?"

Mary is soon written off by Hilary Faye and her entourage after one public expression of religious doubt. But her soul finds refuge, and more than a little worldly enlightenment, under the wings of two rebellious campus outcasts, played with amusing subversiveness and surprising virtuosity by Eva Amurri ("The Banger Sisters") and Macaulay Culkin -- yes, that Macaulay Culkin.

He comes close to stealing the movie at times as cynically easy-going, securely secular Roland, Hilary Faye's wheelchair-bound brother who, in his sister's eyes, isn't thankful enough for her good-Christian sacrifice of accepting a handicap-equipped van for her 16th birthday instead of a sports car. Amurri is Cassandra Edelstein, the school's token Jew and a total sexpot. "Everyone wanted to get her saved!" Mary exclaims in her emerging-from-obliviousness voice-over.

Dannelly's wicked sense of humor ("Anything yet?" Mary asks hopefully while letting the boyfriend feel her up) and wickedly smart casting (the amazingly self-possessed Malone perfectly embodies ingenuous Mary, who isn't self-possessed at all) both compliment the fact that despite all the jokes aimed at judgmentalism, religious faith itself is not under attack in this movie.

While "Saved!" certainly mocks that seemingly impenetrable bubble of quaint naiveté that often surrounds Christian youth, the devout in this picture are well-rounded and well-drawn characters. This is true even of Hilary Faye, who at least believes she's doing the Christian thing -- right up until she snaps out of frustration with Mary's perceived slide into heathenism and throws a Bible at her screaming, with uproarious irony, "I am filled with Christ's love!"

But as the film moves into its third act, it loses its voice and its teeth -- just as Mary is finding those qualities in herself. Hilary Faye de-evolves into an over-the-top teen movie queen-bee villainess, and Dannelly falls back on problematic plot devices and conventional comeuppance, opting for easy answers, prom-scene showdowns and a pat conclusion.

This sitcom-y decline in creativity is especially disappointing since the cast tries hard to stay true to the smarter spirit that was clearly intended. But "Saved!" does remain funny from start to finish, and that's its saving grace.