Good scripts don’t over-explain. They leave mysteries for us to speculate about, mull over, mysteries that draw us in.

“Little Sister” is slight, unfussy character study with a hint of such mystery. It’s about a 21 year-old novice nun estranged from her family for three years. Colleen (Addison Timlin)  ran away to join a convent.

Why? We don’t really learn the “big mistake” that hurled her into the arms of religion. But when we meet her family and get a taste of her past, we get hints.

Sister Joan is about to take her vows. She reads to the sick, buys food and feeds the poor and seems to walk the walk and talk the talk. But she still hangs out with people her age, experimental theater types who ridicule the Bush Administration (It’s 2008) on-stage, and offer the nun-to-be “blow” offstage.

And as is often the case in movies about nuns — “The Sound of Music” wasn’t the first — her Mother Superior has her doubts about the girl. Barbara Crampton, flinty but much prettier than the typical movie Mother Superior,  lays down the lay to Colleen/Joan.

“It took God six days to create the universe. You should be able to get your act together in five.”

Go home, see the family you don’t talk to. Take my car.

So Colleen returns to Asheville to deal with her mercurial, medicated mom (Ally Sheedy), her adoring, indulgent dad (“Pieces of April” director and “What’s Eating Gilbert Grape” writer Peter Hedges), her brother and her past.

That past is first confronted when she returns to the darkly-decorated (black paint, upside down crucifix) bedroom she abandoned for the nunnery. She runs into people who knew her, and then an old friend from “back then” (Molly Plunk). They’re not used to seeing her buried under pancake makeup, her hair dyed some unnatural color.

Back in the day, Colleen was an Asheville Goth.

Evening meals, which she insists on praying over, show how far she’s left all that behind.

But her beloved older brother (Keith Poulson) is a Marine, returned from Iraq burned and scarred for life. He’s crawled into his garage apartment, alone with his thoughts, his old GWAR horror-metal CDs and his drums. He seems lost and doomed, self-aware enough to not wallow in self-pity, not wanting anybody else’s pity either.

Joan will need her inner Colleen to draw Jacob out.

“Sister” has that “film festival movie” tone to it, where nothing much happens — character arcs are limited and narrow — but carefully observed details and personality quirks keep you interested. Almost every character on the screen feels lived in.

Timlin, of “That Awkward Moment” and TV’s “Zero Hour,” has a wounded winsomeness that is quite winning. Poulson registers some emotion underneath his “Deadpool” mask, and Kristin Slaysman makes a lasting impression as the sexy fiance who refuses to abandon Jacob even if that’s what he wants, even if her sexual frustrations are getting the best of her.

Sheedy, decades beyond her “Breakfast Club” heyday, still brings the brittle. Her Joani (A convent clue?) has a fierce and formidable narcissism that cannot understand Colleen’s choice and refuses to accept the uptight religious woman her daughter turned into, something she lashes out about in between medications.

“I will try to correct myself, with the grace of God,” is exactly the sort of reply that will set her off.

The script has the odd zing, even if it never quite dazzles. Writer-director Zach Clark isn’t above going twee and cute — a lip-syncing Goth moment, a high school crush acted-on. And the whole “hope/change” election year setting seems obvious and pointless.

But even without big revelations or surprises, it’s not without its charms. “Little Sister” levitates above the trite and banal, even if it never quite takes flight.

MPAA Rating: unrated, with drug use, adult situations, near nudity

Cast: Addison Timlin, Ally Sheedy, Keith Poulson, Peter Hedges, Barbara Crampton, Kristin Slaysman, Molly Plunk

Credits:Written and directed by Zach Clark. A Forager/Wraith release.

Running time: 1:31