Is she savior or menace?

Losing our moorings inside a Los Angeles-based cult.

Brit Marling starred in and co-wrote last year's Another Earth, an emotionally devastating bit of sci-fi built around real human emotion, namely the guilt experienced by a young woman who caused a fatal automobile accident. With Sound of My Voice, Marling again appears in a movie in which a mild sci-fi hook jump-starts a story that's more focused on probing human behavior than on speculating about the future.

Sound of My Voice doesn't have nearly as much emotional heft as Another Earth, but it's constructed in ways that keep us guessing about where our sympathies rightly belong. Director Zal Batmanglij, who co-wrote the script with Marling, does a good job of creating a world that feels as if it has been cut off from the rest of life and put under intense scrutiny.

Broken into 10 sections, the story begins when a couple (Christopher Denham and Nicole Vicius) decides to go undercover to make a documentary aimed at exposing what they believe to be a dangerous cult.

In the movie's compelling opening scenes, Denham's Peter and Vicius's Lorna are blindfolded, bound and taken to a modest suburban Los Angeles home. There, they're asked to shower and put on hospital gowns. The vibe is borderline hostile, and if we didn't know that Peter and Lorna were acting of their own volition, we might think they'd been kidnapped.

Enter Maggie (Marling), an attractive blonde who's hooked up to an oxygen tank. Little by little, Maggie tells her story, which revolves around her claim that she has been transported from the future into our present.

With help from a bearded associate, Maggie has begun to gather a small group of devotees, pledging to prepare them to survive a time when the country will be torn apart by civil war, and scarcity will become the order of the day. No one discusses religion.

Scenes in which Maggie works on her charges can be gripping, particularly one in which she gradually peers into Peter's past. She tries to force Peter to purge his weaknesses and fears by literally vomiting them up.

A picture such as Sound of My Voice only can work if we entertain the possibility that Maggie is telling the truth about herself. Marling's performance makes that possible. Her Maggie is alluring, insightful and slightly ethereal. She has an obvious gift for looking into people's hearts, breaking them down and rebuilding them for the challenging new future they're supposedly going to face.

To its credit, the screenplay never bothers to dot every "i" and cross every "t," but it's clear from the start that Peter and Lorna -- like us -- must grapple with their sense of certitude.

You don't need to know much more to become caught up in the game that Batmanglij plays right up until an ending which -- if not exactly mind-blowing -- has a definite kick.