Even now, Jessica Chastain can summon up Khalid Sheikh Mohammed's face. "KSM, Abu Faraj, all of them – they're still there, in my head," she says. It's a December morning, and the actor is recalling a technique she used to enter the obsessive brain of Maya, the CIA operative Chastain plays in Kathryn Bigelow's Osama bin Laden thriller, Zero Dark Thirty: During shooting, Chastain hung "photocopied, grainy pictures" of Al Qaeda members on the walls of her hotel room, forcing herself to live with the faces the way her character does. "I approached it as 'It takes a fanatic to catch a fanatic,' " she says.
Chastain has just woken up in her downtown Manhattan apartment, which she shares with her three-legged rescue dog, Chaplin – and which is, she's happy to say, terrorist-photo-free. "It’s very spa-like, very simple," she says. "When I finished shooting Zero Dark Thirty, I threw everything away. I needed to wash myself clean." It will be a while before Chastain can put Maya fully behind her, though – at least until the Oscars, where she's a strong favorite for Best Actress. A Juilliard graduate from Northern California, Chastain, 35, broke big in Terrence Malick's 2011 family saga, The Tree of Life, inhabiting a woman she characterizes as a "graceful, perfect, devoted mother," opposite Brad Pitt. But she quickly became known for her versatility. Her post-Tree of Life roles – including The Help, Zero Dark Thirty and the new Guillermo Del Toro-endorsed horror-fantasy film, Mama – were chosen in part to avoid becoming known as a go-to angelic mom. There is nothing angelic, of course, about Maya, and it's no small irony that Chastain, a self-described "hippie vegan girl," starred in a film whose depictions of "enhanced interrogation techniques" have been criticized as endorsements. "This film does not condone torture," Chastain says. "This is part of our history, this is what we did, and the question Kathryn leaves us with at the end is, 'Where do we go from here?' "
This story is from the January 31st, 2013 issue of Rolling Stone.