Sarah (Brit Marling), an undercover agent at a private intelligence firm, is hired to infiltrate the East, an ecoterrorism cell targeting companies that pollute the environment. Though one (Elliot Page) of the group's hardcore members is suspicious of her, Sarah manages to win over Benji (Alexander Skarsgård), the East's leader. However -- even as Sarah tries to maintain her cover -- she gains more sympathy for the group's cause while, increasingly, becoming drawn to Benji.