The mechanics of cults appear to fascinate writer-director Zai Batmanglij and his co-writer and star Brit Marling. In “Sound of My Voice,” their first collaboration, they focused on an underground group headed by a woman who claims to be from the future. Now in “The East” their subject is a secretive organization of eco-activists ready to use extreme methods to stop polluters and their government protectors. Though not a cult in the conventional sense, it certainly has many of the attributes of one. And its inner life is revealed with the same sort of unnerving sedateness here that the group’s practices were in the earlier film. Apart from that, however, this political thriller stumbles over the ordinary things—the genre conventions that should be taken for granted. It’s an odd blend of sophistication on one level and maladroit technique on another.

Marling stars as Sarah, an employee of one of those private security firms to which the government has taken to outsourcing many of its intelligence activities. She’s chosen by her coldly rational boss Sharon (Patricia Clarkson) to go undercover and infiltrate The East, an environmental group that’s targeting energy and chemical conglomerates. Telling her supportive boyfriend Tim (Jason Ritter) that she’s going off on an assignment in the Middle East, she actually takes on the persona of an activist herself, engaging in activities that earn her the grudging trust of the East’s members and an invitation to the collective’s secluded estate in a heavily-forested enclave.

It’s here that the film is at its most fascinating as Sarah is introduced to the group’s mode of life, which hearkens back to the communitarian style of sixties radicals. A dinner-table scene is simultaneously creepy and oddly charming, as is a game of spin-the-bottle played by members as a sort of group support session. In these sequences Batmanglij’s touch is as assured and effective as it was in similar moments of “Sound of My Voice,” and Marling conveys Sarah’s growing ambivalence about these people nicely.

She becomes particularly intrigued with Benji (Alexander Skarsgard), the quietly charismatic leader of the group (and, as it turns out, the owner of the estate) who treats her with respect, even enlisting her in operations. His attitude contrasts with that of Izzy (Ellen Page), a firebrand with an agenda of her own, who’s not at all certain of Sarah’s reliability. Other members of the group—like Doc (Toby Kebbell) and Luca (Shiloh Fernandez)—come across as individuals in their own right rather than mere props, too.

But as Sarah’s allegiances shift, in a predictable plot device, the picture tends to become ever more schematic and the dialogue increasingly obvious. It doesn’t help that when the film moves beyond the compound to portray assaults mounted against industry tycoons, the skillfulness of execution declines markedly. Indeed, these sequences look pretty threadbare, in purely visual terms, and aren’t particularly well choreographed. The same might be said of the federal assault on the estate (using, it would appear, a single run-down van), and Sarah’s last-act attempt to retrieve important data for Benji from her company’s heavily-protected headquarters. Neither sequence generates anywhere near the excitement or suspense it should. And a last-minute revelation about Benji’s motives comes off as an almost cynical throwaway.

Marling’s performance weakens along with the narrative, but she remains an actress of strong potential, and Skarsgard certainly makes an interesting presence, though in his hands there’s a lackadaisical quality to Benji that does seem to fit the character. Page is properly ferocious, and Clarkson coolly malevolent, and the other members of the group certainly acquit themselves adequately. But some of the smaller roles aren’t well filled, and though technically this is clearly a step up from the bargain-basement “Sound of My Voice,” it still shows obvious signs of budgetary limitations.

The many moments of insight and invention in “The East” go far to redeem an uneven film. But they don’t quite compensate for the deficiencies.