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In episode eight of Showtime's award-winning series Homeland, there is a poignant scene in which CIA officer Carrie Mathison, played by Claire Danes, speaks with her boss and mentor Saul Berenson (Mandy Patinkin) about love and its close cousin, loneliness. Danes's character is secretly bipolar and has fallen hard for a Marine she also suspects of being a terrorist; Berenson's own wife has just left him. When she tells Berenson she has had an epiphany of sorts—"I'm gonna be alone my whole life, aren't I?"—the bereft Saul doesn't answer; they just look at each other in silence. The camera pulls back, and there is this brief but oddly affecting—and, as it turns out, completely unscripted—moment when Danes, whose legs are crossed, slowly lifts her right calf in a sort of absentminded stretch that the viewer watches through the vertical blinds of the office.

"It was so perfect," says executive producer and cocreator Alex Gansa. It also was one of the most internally debated gestures on a show in which there is an abundance of far more debatable actions and subjects. Chip Johannessen, the show's coproducer who wrote the episode, "had an hour-and-a-half-long argument with the editor about whether or not to keep [the move]," Gansa says. "Finally, after adding the final scene with [Sgt. Nicholas] Brody, they took it out, but we all agreed that something was missing." It was a tiny thing, he admits, but it sent a clear signal— and ultimately, it was put back in. "It was like, ‘Yes, I've had an epiphany, but it's not as heavy as all that.' Claire always finds something that's unique and signature."

Television is where Danes—whose film credits include Little Women, Romeo + Juliet, and The Hours—has always found her signature roles. At 14 she originated the role of angst-ridden teenager Angela Chase in My So-Called Life, the ABC melodrama that lasted only 19 episodes but became a cult classic. In 2010 she played the autistic animal scientist Temple Grandin in HBO's movie of the same name. Danes won an Emmy for the latter, a Golden Globe for both, and added a third Golden Globe this year for Homeland, which also won for Best Dramatic Series.

The complicated and occasionally unlikable role of Mathison, Danes says, was "impossible to ignore." It was also written with her in mind: Gansa and cocreator Howard Gordon, who worked together on The X-Files and 24, were "tremendous fans since My So-Called Life," says Gansa. "We had a wish list, and she was at the top of it; we even named the character Claire in early drafts."

Part psychological drama, part police procedural, and part political thriller, Homeland is almost relentlessly focused on character, and the fact that it airs on Showtime, rather than a commercial network, means that its writers have the luxury of developing what Gansa calls the "smaller, more personal stories." To get at Carrie's narrative, Danes studied up on two subjects previously foreign to her: espionage and bipolar personality disorder. "I burrowed into a lot of literature," she says, adding that she talked the members of her Manhattan book club into taking on some of her research materials at their monthly meetings. "I like nerding out and getting a chance to delve into something I otherwise wouldn't learn about."