Sound of My Voice (15)

Starring: Brit Marling, Christopher Denham

The search for meaning can take people to the oddest places. In Zal Batmanglij's debut feature, a psychodrama with a sci-fi reverb, two people seek the truth inside a nondescript basement somewhere in suburban California.

Peter (Christopher Denham) and his girlfriend Lorna (Nicole Vicius) are among the latest recruits to be inducted into a cult. T3hey are driven blindfolded to a mystery location, told to strip and shower, dressed in white hospital gowns, then led down to a basement where they exchange an elaborate handshake ritual that's so close to a Three Stooges routine you'd laugh out loud. Except that nobody here does. Enter a serene, floaty young woman in white, trailing an oxygen tank. This is Maggie (Brit Marling), leader of the cult, who claims to have come from the future – 2054, to be precise – and speaks in a soothing, tell-me-your-troubles voice, though the news she brings is not good: civil war lies ahead, and they must save themselves from oblivion.

Maggie's followers, seated cross-legged on the floor, absorb this message with expressions of great solemnity. So do Peter and Lorna, until they get back home and play a recording of their strange encounter. These two, you see, are undercover film-makers who have posed as neophytes so as to gather material for a documentary expose. They both agree that Maggie is "dangerous", though Peter is the more sceptical and scornful investigator; he's determined to show up Maggie as a charlatan, and he takes the risk of smuggling in the technology to do it. The divergence in the couple's perception of their inscrutable subject becomes a dramatic pivot of the movie, the second this year, after Martha Marcy May Marlene, to focus upon the inner workings of a cult.

The most salient difference between Sound of My Voice and Martha Marcy... is in the charismatic leader being a woman rather than a man. In the latter, John Hawkes was a soft-spoken predator who ruled his mostly female flock through sex and intimidation. Brit Marling, who also co-wrote the script with Batmanglij, is a more touchy-feely presence as Maggie, a doe-eyed high-priestess who asks questions like, "How do we rise to our callings as chosen ones?" Er... She has her own powers of manipulation, though, exhibited in the "purging" rituals she conducts on her disciples: on her command, each vomits up an apple they've just eaten. All but Peter, who says he can't, at which Maggie turns mystic, stripping down his psychological defences and divining an abused childhood he's never admitted to Lorna, or even perhaps to himself. (He duly barfs). He later claims this confession to be made up, a way of winning Maggie's trust, but by now the leader/disciple relationship is so convoluted we can't tell if he's lying or not.

The film is deadly serious in its way, yet it keeps picking up weird comic vibrations from the creepiness. The conspiratorial handshake – a superMasonic, you might call it – doesn't get any less absurd, while Maggie's testing of her followers' gag reflex with "live" food starts to resemble a gameshow – "I'm a Cult Member, Get Me Out of Here". This time I did laugh, when one of the more squeamish takes a look at what Maggie wants them to eat and says, "I'm vegan." The best scene, though, is one that answers to our own curiosity about Maggie's outlandish claim of time-travel. During a group Q&A about the future, one disciple asks her whether there's music in 2054. When it's established that there is, another man asks her to sing something that's popular "there", a request that's perfectly genuine but also pitched to test her credibility. After some cajoling, Maggie agrees to sing, and warbles out a quite ordinary little love song. Well, sounds OK, you think – until the man, with a puzzled look, announces that the song, actually, is by Irish pop group The Cranberries, and was a hit in the 1990s. How does she get out of that one?

Doubts begin to breed within the hothouse atmosphere. Is Maggie a fraud, a nutter, a narcissist, a fugitive from the FBI? Or is she – dramatic pause – something altogether different? Peter and Lorna are baffled, as we are, and their partnership starts to fray under the pressure. Batmanglij turns his low-budget settings to advantage, building tension with thumping chapter intertitles and unsettling incidental music (by Rostam Batmanglij). The plot takes a sinister turn when Peter is compelled to involve one of his eight-year-old pupils (he's a supply schoolteacher in "normal" life). Sound of My Voice has achieved its effects up to this point with such deft economy that you feel something memorable, and perhaps horrible, is on the way.

It doesn't work out like that. Having paced it carefully, the film-makers hurry through the denouement as if they'd been told to wind it up that minute. They have a surprise in store, but it's also a bit of a cheat. The tension the film has mined between rationality and the need to believe in something is not an easy one to resolve, but it deserves a subtler payoff than it gets here. Most films are too long. This one feels about 20 minutes too short. (Did they simply run out of money?). Praise all the same to Batmanglij on his debut, and to Marling for a performance to match her guilt-tormented astronomer in a similar alt.sci-fi psychodrama, Another Earth. I'm pretty sure she's not come from the future, but the future may be coming for her.