Two years ago, Brit Marling’s was the biggest story of Sundance: a gorgeous Georgetown University valedictorian turns down a job offer from Goldman Sachs to write and star in a pair of critically acclaimed festival films, as a cerebral woman scarred by a tragic event in Another Earth, and a charismatic cult leader in The Sound of My Voice. Last year, in a cheeky nod to her finance past, she appeared in the Sundance flick Arbitrage that simultaneously humanized and demonized a Bernie Madoff–type, played by Richard Gere.

Marling has reunited with her Voice director and co-writer, Zal Batmanglij, in The East.

The film, again co-written by Marling, stars the actress as Sarah, an agent for a private security firm, who is tasked with going undercover in a dangerous eco-terrorism cell that calls itself “The East.” Ambitious, religious, and D.C. preppy, Sarah is forced to trade in her heels for Birkenstocks by her hard-nosed boss, played with glee by Patricia Clarkson. The East has been wreaking havoc on many of the security firms’ clients, including flooding a big oil exec’s posh Hamptons pad with crude oil.

Sarah eventually makes her way to The East’s ramshackle headquarters, located deep in the forest, and is forced to endure a series of psychological manipulations in order to gain their trust—including a tremendous set piece involving straitjackets and ladles. It is here, as Sarah ingratiates herself to this gang of renegade, New Age idealists, including the skeptical Izzy (Ellen Page), a doctor with a troubled past (Toby Kebbell), and Benji (Alexander Skarsgard), the gang’s attractive and mysterious ringleader, that the film really soars, as the double-agent must reconcile her mission with that of The East, whose ethos of punishing dangerously negligent pharmaceutical and energy companies starts to rub off on her.

Batmanglij’s direction is first-rate. Unlike his aforementioned previous film, The East is a very slick-looking thriller—Ridley and the late Tony Scott, after all, produce it—and moves at a very fluid pace (save a bit of second-act dragging). The music is also mesmerizing, most notably a frenetic, haunting piano solo by Kebbell in this, a thoroughly engrossing mash-up of Martha Marcy May Marlene and Serpico. But the film is, first and foremost, a wonderful showcase for Marling’s considerable talents. The 29-year-old actress has created a fully formed character in Sarah, who possesses great psychological and physical strength yet, like most real people, is filled with fascinating contradictions. Marling isn’t a bona fide star yet, but you may as well consider this her big coming-out party.