Jessica Chastain landed the lead role in "Zero Dark Thirty" at the end of a crazy year in which she’d appeared in two Best Picture nominees, "The Tree of Life" and "The Help" (winning an Oscar nominaton for the latter), along with "Take Shelter," "Coriolanus," "The Debt," "Wilde Salome" and "Texas Killing Fields."

And while 2012 didn’t see as many releases, it brought "Lawless," "Tar," the lead role in a new Broadway production of "The Heiress," her voiceover work in "Madagascar 3" — and, towering over the rest, her performance in "ZDT" as Maya, a fictionalized version of the dogged CIA agent who spearheaded the hunt for Osama bin Laden.

The character is something of a machine and the role a cipher, but Chastain is remarkable as the cold, relentless heart of a decade-long manhunt.

Kathryn Bigelow’s movie has been a lightning rod for controversy since it began screening, but it has also won more critics' awards than any other film from 2012 — and it instantly puts the 35-year-old Chastain among the top ranks of Best Actress contenders.

You did the movie right after going through the craziness of last year's awards season, didn't you?

Yeah, it's crazy. I was at the Oscars drinking champagne with my grandfather in my Alexander McQueen dress, thinking, This is amazing. And the next day I got on a 25-hour flight to India. I landed and called the set, and jokingly said, "OK, guys, I'm ready." They said, "Come to the set now," and I immediately went without hair and makeup and started shooting.

They had already begun production?

They started two days before me. It was a very condensed schedule, because we didn't want the information to get out about what we were filming. And we were filming in a difficult part of the world: I'd go to lunch with Jason Clarke and the Edgerton brothers, and the waiter would bring three menus for the guys and nothing for me.

For part of the time we were 150 miles from the border of Pakistan. So you could imagine what would happen if word got out that this movie was about the 33-year-old woman who found and led the mission to kill bin Laden. We really wanted as little publicity as possible.

Also read: Kathryn Bigelow Denies 'Zero Dark Thirty' Apologizes for Torture (Exclusive)

While the film was shooting, people assumed that you were playing a supporting role to the guys who brought down bin Laden. Now it turns out that you’re the lead.

I hated not being able to tell anybody about who I was playing. Most people assumed I was playing Joel Edgerton’s wife. You think that in a movie like this, the girl is going to be the wife, and anytime anyone made that assumption I’d think to myself, That’s so not true. But I couldn’t say anything. And I’m terrible at keeping secrets.

And now you can say some things … but not everything, right?

I know things about the real woman that I can’t say. I did not meet her, but I did a lot of research and talked to a lot of people who were involved. But it’s difficult because there are active members of the CIA depicted in this movie, and it’s very important to protect them.

It’s a major concern to all of us that this woman, whom I see as a great hero, not be punished because of this story coming to light.

Is much of your characterization based on the real person?

A lot of it is, but I had to fill in a lot of blanks. I was really moved by the idea of this girl being so driven, yet becoming almost nothing. So the voice I use, the hair changes and the costume changes, those are all deliberate choices. When we first see her there’s femininity, a youthfulness.

The colors are warm, and then as the movie goes on I wanted to make her sexless. It’s the sense that she’s become nothing except for this project.

In one scene, we see a screensaver on her computer that has a picture of her and a younger girl. It’s really the only sign that she has a life outside of this manhunt.

There are little things that hint at what she was once was. There’s the scene when she asks for candy from back home, and she’s eating licorice and peanut M&Ms. Or when they say, “Hey, have you and Jack hooked up?”

Also read: 'Zero Dark Thirty' Review: Like a Really Good 'Law & Order' – With Waterboarding

And there’s a lot of that [sex with colleagues] going on around her, but this girl wouldn’t even consider that because she doesn’t want to be known for it.

It’s funny, because the character couldn’t be further from my life: I’m a vegan, I’m not someone who thinks about targeting or killing people. But for me this movie was about the absolute sacrifice of self, and I connected to this character a little bit in certain ways.

When I got into the business I never wanted to be involved with an actor, or director, and I didn’t want people to know about my personal life. I want to be known for my work. So when I approached this role I was like, “Oh my God, I get this.” I get this idea of, I’m going to give you what I am, I’m a servant to this, and that is all you’re going to see.

Is there extra pressure, playing a real person and chronicling such a key historical moment?

Well, it’s a big responsibility, this movie, because of the moment in history that it represents — but also, when I read it I thought this woman was an incredible character. Of course, I thought of Jodie Foster’s role in "Silence of the Lambs."

I guess the difference is that the social skills of Maya are completely nonexistent. She’s a computer. I thought of when I was going to Julliard, and I used to play a game where I’d sit in the cafeteria and you could always tell which department people were in. The actors were the loudest and most obnoxious, the opera singers had scarves and there was something grandiose about them, the dancers had hardly any food and they were small.

And you could tell the musicians because they were very awkward. They spent their time in their rooms with their instruments, and that’s how I thought about Maya. She spent her life in her room learning things.

After the movie was finished, the book "No Easy Day" came out, with a description of a CIA agent the author calls Jen, who clearly seems to be the same person the movie calls Maya. And since then there have been other stories about that woman, and how she's driven and unsociable and not liked within the agency.

I think it's great that information is coming out about her. I was talking to Kathryn [after a Washington Post story came out], and she said, 'Everything in the story sounds just like our character."

And in the book, everything he wrote about Jen is right on. I have a copy with a post-it note on every single page where she is mentioned, and I thought that the way he spoke of her was with great respect. You have this Navy SEAL who was there say, "This girl was on this for seven years — we were on it for 40 minutes."

The torture scenes are graphic and tough to watch. How were they to shoot?

Oh, it was very grueling. We shot those in a prison in Jordan, and it was scary to even be there. You couldn't bring a cell phone in, and when you walked in you had to go past all these little cells with guys looking out. I don't know if it was an actual site where they did interrogations, but I know Mark and Kathryn tried to be authentic.

You filmed all those scenes in one stretch at the beginning of the shoot, didn't you?

Yes. It was a loss of self to me to be there. Doing the torture scenes, it was just me in that room watching what they were doing. There was one day on set where I just felt so tired and sad and lonely, and I needed five minutes to walk away from the set and have a big cry. It’s a tough movie for me to watch, too. It looks like I’m about to have a nervous breakdown, and in ways I felt like I was.

But that worked for the character because this movie is all about subtext. It’s about this incredible loneliness as she keeps fighting and spiraling down while people around her are covering their asses.

You can see the stress in my face. I had to do whatever I could to keep it up, because Maya kept it up. She was always 100 percent there. There were times when Jessica was feeling like, I’m a horrible actress, I suck, why did they hire me? But I had to get to that place and believe in myself.