"There were all these versions of Lisbeth Salander, but the one that had the most layers was Rooney's," says director David Fincher. Alexander Wang knit top. Fashion Editor: Tonne Goodman.

It’s approaching midnight, and the June sun is winking on the horizon, still hoping to conjure one last moment of spooky beauty for the good people of Stockholm. Rooney Mara, David Fincher, and I are walking home from a two-bottle-of-wine dinner at their favorite café, around the corner from Ingmar Bergman Plats. Both of them have been living in Sweden, on and off, since the previous summer, shooting one of the most anticipated movies in years: The Girl with the Dragon Tattoo. As we pass the Royal Dramatic Theatre, where Greta Garbo studied as a teenager, Mara points to the clock tower in Gamla Stan, silhouetted in the distance, and reminds Fincher that when it strikes twelve it will be exactly one year to the day since he first auditioned her to play the part of Lisbeth Salander, arguably the most coveted role for an actress since Scarlett O’Hara in Gone With the Wind (another film adaptation of a wildly popular book featuring a shrewd, complicated, difficult-to-love heroine capable of slaying a man).

“Really?” says Fincher. “A year ago tomorrow?” He shakes his head in disbelief and then fishes a vibrating phone out of his pocket: “Hello, Amy.” It is the co-chairperson of Sony Pictures, Amy Pascal, the studio head who, if this movie takes off, will surely get credit for having greenlighted the first truly adult franchise to come out of Hollywood since the early seventies, when movies like The Exorcist—not Twilight—were winning the terrified hearts of audiences everywhere.

Mara and I drop back to give Fincher some privacy—though we can still hear snippets of his conversation. “It wasn’t supposed to be released!” he says into the phone. Mara laughs. “I think they are talking about my boobs right now,” she says with deadpan resignation. Turns out an explicit version of the movie poster, in which Mara’s breasts (and pierced nipple) are exposed, was leaked on the Internet today. “There’s a certain way people are used to seeing nude women, and that’s in a submissive, coy pose, not looking at the camera,” Mara says. “And in this poster, I’m looking dead into the camera with no expression on my face.” She smiles and flicks a cigarette into the street. “I think it freaks a lot of people out.”

When The Girl with the Dragon Tattoo is released on December 21, boobs on a poster will be the least of anyone’s concerns. In case you have somehow missed it, Swedish writer Stieg Larsson’s novel of the same title, published posthumously in 2005, may well be the unlikeliest runaway best-seller in publishing history, filled as it is with impossible-to-pronounce Swedish names, nefarious financial intrigue, festering Nazism—and some of the most disturbing sexual violence imaginable. As The New York Times put it, “The novel offers a thoroughly ugly view of human nature.” Though Dragon Tattoo is, at its core, a conventional thriller crossed with an old-fashioned murder mystery, the book, like its writer, is bizarrely preoccupied with graphic violence against women. (Larsson supposedly witnessed a gang rape when he was fifteen and never forgave himself for not intervening to help the girl—named, you guessed it, Lisbeth.) Indeed, the infamous rape and revenge scenes in the book are so painstakingly realized on the page that it’s hard not to wonder if Larsson was indulging a few submerged fantasies of his own. Despite all this, the so-called Millennium Trilogy (which includes The Girl Who Played with Fire and The Girl Who Kicked the Hornet’s Nest) has sold more than 50 million copies worldwide.

At the center of all of this howling evil is the strangely relatable Lisbeth Salander, a damaged, vengeful, brilliant, androgynous cipher—a wholly original literary character, and Larsson’s real contribution to the pop-culture canon. She is the reason that people can’t put these weird books down—and why David Fincher, one of the most sought-after directors in Hollywood, signed on to the franchise, despite its many inherent challenges. As Fincher said earlier at the restaurant, “Look, there are parts of the book that I don’t love, and parts of it that make it a maddeningly difficult story to turn into a movie. We are walking in other people’s footsteps, and we have to be careful.” He is referring to the fact that a lot of people already love the Swedish film versions. “I am a contrarian by nature, so all it does is make me want to take real risks. I am like, ‘If we are not out on the ledge juggling chain saws, then we are doing ourselves a huge disservice.’ ”

As Fincher talks about the film, his heroine, Mara—with Salander’s awesomely strange hair, bleached eyebrows, and facial piercings—sits next to him, looking for all the world like a troubled college student who takes too much Adderall. She hangs on his every word, her eyes lit with admiration. Their relationship, it quickly becomes clear, is charged with the electric current of the mentor-protégée crush, which is both touching and occasionally uncomfortable to watch. Or, as Daniel Craig, who costars as a crusading journalist named Mikael Blomkvist, says about their working relationship, “It’s fucking weird!”

When a waiter appears to take our order, we are all looking at our menus, but I see out of the corner of my eye Fincher nudging Mara. He says with quiet seriousness, “You can eat.” I look up to see her reaction. Mara rolls her eyes, and Fincher laughs. “You can have lettuce and a grape. A raisin if you must.” She orders a piece of fish and barely touches it. In the book, Salander is described as boyish and awkward, “a pale, anorexic young woman who has hair as short as a fuse. . . .” Noomi Rapace, the magnetic star of the Swedish versions, looked more like Joan Jett. “One of the things that make our version that much more heartbreaking,” says Mara, “is that even though I am playing a 24-year-old, I look much younger. I look like a child.” I ask if she had to get unhealthily skinny for the role. She says, “Umm . . . not really.”

“It hasn’t been too hard for her,” Fincher quickly adds.

To tell the story of how Rooney Mara landed the role of Lisbeth Salander, one must go back to David Fincher’s last film, The Social Network. That movie, as you may recall, opens with five minutes and 22 seconds of blistering dialogue between Mark Zuckerberg (played by Jesse Eisenberg) and his fictional college girlfriend, Mara’s Erica Albright, on a relationship-ending date in a pub. “I remember the feeling that I needed a foil for Jesse and his intense inability to see other people,” says Fincher. “I needed somebody about whom the audience could go, ‘Dude! She’s right there!’ ” Radiating intelligence and self-possession, Mara was a natural for the part.

Then, as Fincher was putting the finishing touches on the film, he started casting Dragon Tattoo. “I had seen a lot of actresses,” he says. “I was beginning to get to the point where I was thinking, Maybe conceptually you are talking about a person who doesn’t exist.” One day his casting director said, “What about Rooney?” He resisted at first. “I believe in casting people whose core—that essential personality you can’t beat out of them with a tire iron—has to work for the character.” He needed someone who was dissociated, antisocial—the exact opposite of Erica Albright. But when he saw Mara’s audition, he was “struck by how different it was from what I felt I already knew about her.”

Mara pipes up: “You didn’t really know me at all, though.”

“I worked with you enough to have an opinion,” he says.

“I was only on The Social Network for four days, so I didn’t really get to know anyone,” says Mara.

“Twenty-four hundred takes,” says Fincher.

“Twenty-four hundred takes but only four days,” says Mara.

“It was a foundation,” says Fincher. “It was a, Wow, here’s someone who just keeps trying. Try this, try this, try this. . . . ”

And so began an agonizing period for Mara. “It was like, ‘Come in. We need you to do this, we need you to do that.’ That’s all I thought about and all I did for weeks.” She mentions a time Fincher said, “Go out and get really, really drunk and come in the next morning so we can take pictures of you.” He wanted to show Sony that she could look strung out. “And I did it!” says Mara. “Threw up all night!”

Meanwhile, Fincher was also screen-testing every conceivable Salander on the planet. “We flew in people from New Zealand and Swaziland and all over the place,” he says. “Look, we saw some amazing people. Scarlett Johansson was great. It was a great audition, I’m telling you. But the thing with Scarlett is, you can’t wait for her to take her clothes off.” He stops for a moment. “I keep trying to explain this. Salander should be like E.T. If you put E.T. dolls out before anyone had seen the movie, they would say, ‘What is this little squishy thing?’ Well, you know what? When he hides under the table and he grabs the Reese’s Pieces, you love him! It has to be like that.”

Mara, it seems, had the right combination of lovability and strangeness. “There were all these different versions of Salander, but the one that had the most layers was Rooney’s. I kept coming back to this.” He gestures theatrically toward Mara as she stares at the table with a big grin on her face. “I thought, This is the person to follow.”

The day she got the part, Fincher called Mara into his office. “I said, ‘I need you to come in so I can get a photograph of you on a motorcycle.’ ” Mara was annoyed. “I was ready to throw down,” she says. “I was thinking, You either think I can be this girl or you don’t, but I need to move on with my life. He sat me down and gave me this long spiel about all the bad things that are going to come to whoever plays this part. He said something like, ‘Vivien Leigh was incredible in A Streetcar Named Desire, but she will always be Scarlett O’Hara, and you need to be prepared for that.’ ”

Fincher laughs: “Yeah, and I also said, ‘Have you given any thought about what it’s like to be Ginger on Gilligan’s Island? You may never get out from under it. Are you willing to put your head down, do the hard work, not go crazy?’ ”

Fincher seems pretty confident he picked the right girl. When Mara excuses herself from the table for a moment, he turns to me. “Oh, man,” he says, smiling. “She’s a weirdo. She’s a great weirdo.”

The next afternoon, Mara and I go to Stockholm’s famous food hall, in the ritzy Östermalm neighborhood. Although she stands out among the sea of blond giants like a tiny chic ghoul, no one gives her a second glance. Far be it from these urbane Swedes to ever betray any discomfort with an “outsider.”

Lunch in hand, we head to her favorite park—which also happens to be a cemetery—only to find every bench occupied. “Is it weird to sit on a tomb?” she says. “It’s kind of perfect, right?” We walk over to one that is big and flat and low. “Is this a good tomb?” Laughing, we spread out our picnic on top of the ancient stone casket.

Mara is wearing a slight variation of what she had on last night: black leather boots, a pair of gray drop-crotch parachute pants from Zara, and a vintage Swedish military shirt that she pinched from wardrobe. Google pictures of pre–Dragon Tattoo Rooney and you will find a pretty young thing with lustrous brown hair and bright blue-green eyes. “Before, I dressed much girlier,” she says. “A lot of blush-colored things. Now I literally roll out of bed and put on whatever is there. I have really enjoyed being a boy this last year.”

She is referring to her complete physical transformation at the hands of Pat McGrath, the doyenne of haute makeup; rock-diva hairstylist Danilo; and the costume designer Trish Summerville. As Summerville says, “We didn’t want her to be this girl who looks like a musician in a rock band. She’s real. A lot of the time she’s dirty. She wipes her nose on her sleeve.”

Once Fincher approached McGrath, she went straight online to see who was playing Lisbeth Salander. “When I saw that it was Rooney,” she says, “and I saw those bony features, those cheekbones, those eyes, I said, ‘I can’t wait.’ I was instantly inspired. It’s like in fashion, when you get a girl who has one of those haunting faces that you can do absolutely anything with.”

Holed up in a tiny studio for two days with Fincher and Mara, McGrath created about 26 different looks. “We went from the white-powdered sick-clown makeup to stitches in the face all the way to greasy, bloody eyes. I instantly knew how I could make her character so different. And then once the hair was cut in that mad shape, I was like, Well, the eyebrows have got to go. And in the end, it would look now and it would look new.”

Two weeks later, Mara was in a New York hotel room, where Danilo “cut my hair, shaved the sides, bleached the eyebrows, then dyed my hair black,” she says. “Then we went and did the piercings—all in one day. I went in looking like Erica Albright and I came out like this.” Was she traumatized? “The eyebrows were the biggest shock because that really changed my face, and I didn’t recognize myself. But I was fine because I knew it was going to be really helpful for getting into character.”

If it took a lot of work to make Mara look the part, in some ways she already possessed the right stuff. “I am very slow to warm,” Mara says. “I’ve always been sort of a loner. I didn’t play team sports. I am better one-on-one than in big groups.” This, she says, is one reason she gets the character. “I can understand wanting to be invisible and mistrusting people and wanting to understand everything before you engage with the world.”

Born in 1985 in Bedford, New York, to Chris Mara, a vice president at the New York Giants, and Kathleen Rooney Mara, a part-time real estate agent, both now in their early 50s, she has two brothers, Danny and Conor. Her older sister is the actress Kate Mara, best known for her recurring roles on Entourage and 24. Rooney may be new to this, but, through her sister, she has seen how “the football thing” can dominate the conversation.

Mara’s great-grandfathers are Tim Mara, who founded the New York Giants, and Art Rooney, founder of the Pittsburgh Steelers. Because of this lineage, phrases like football heiress and trust-fund baby get thrown around in the press. “I don’t have a trust fund,” she says. “I grew up in a little cul-de-sac in the suburbs and went to public school. I went to Costco on the weekends.” Mara seems almost pained to be so defensive. “When my great-grandfathers founded those teams it cost, like, $500. My dad is one of eleven children. I am one of 40 grandchildren. What bothers me about the whole trust-fund thing is that it sort of presumes that everything is handed to you. And if there is one thing about my family that I do identify with, it is that everyone is extremely hardworking. Also, the people whom I grew up with all did things they really loved. And I think that’s an important lesson.”

Mara and her sister both caught the acting bug from their mother, who took them to Broadway shows and introduced them to old movies. “My sister started acting professionally when she was twelve,” says Mara, “but I wanted to go to college first.” After a year at George Washington University, she transferred to NYU’s Gallatin School of Individualized Study and studied nonprofits and psychology. “I traveled a lot,” she says. “I’d go to Kenya for a month and get credit for that.”

At nineteen, she began auditioning on the side. One of her first roles was on Law & Order: SVU, playing a girl who “hates fat people, and you find out in the end she used to be obese herself. It’s just too embarrassing.” After graduation, she moved to L.A., but pre-Fincher, her biggest role was in the disappointing 2010 reboot of the Nightmare on Elm Street franchise. Mara minces no words about the experience. “I hated it,” she says. “It left me thinking, If this is what is available to me, then I don’t necessarily want to be an actress. And then I got the script for The Social Network.”

No one is more aware of how lucky she is than Mara herself. One of the many blessings (which may yet turn into a curse) of getting to play Salander is that she pretty much knows what she’s going to be doing for the next four or five years. (As somebody on set observes, “She’s going to be stuck with that haircut until 2015!”) She also gets to reside, at least for now, in the family-like cocoon of Fincherworld. Everyone raves about Fincher’s secret weapon, his romantic partner (and producer for the past nineteen years), Ceán Chaffin. A cheerful, formidable presence, she seems to be handling the work of a dozen people, including acting as Mara’s publicist. “She’s incredible,” says Mara. “They are the best people to work with. They will tell you exactly how it is, even if they think you won’t like it. Everything is on the table.” As Daniel Craig tells me, “I wish I’d had someone like David at Rooney’s age just to guide me and say what’s good and what’s bad. You don’t know at that age. You are full of confidence, but you are also full of huge insecurities.”

Mara knows all too well she is breaking out at the very top. “Where do I go from here?” she says. “I’ve been trying to really live in the moment because I will never get this part of it back. As soon as the movie comes out, everyone will turn it into what they believe it is, so I’ve really been trying to appreciate every minute of now. Because I know what’s coming.”

She is perhaps rightfully wary about the media circus that is sure to accompany the film’s release. “That kind of fame is not something I ever wanted for myself,” she says. “It just so happens that this huge, gigantic monster of a film came around that also happens to have the most incredible character that I ever could have dreamed up. But my fear with a movie like this is the kind of exposure you get from it. I think that can be death to an actor. The more people know about you, the less they can project who you are supposed to be. It’s unfortunate that you really only get one shot at that. After this, I won’t be able to be that girl again.”

Fincher answers the door to his lair—an industrial-chic apartment in Södermalm, the edgy (for Stockholm) neighborhood where Lisbeth Salander lives in the book—dressed, as usual, like a teenage boy: sneaks, T-shirt, baggy sweatshirt, and a knit cap that never seems to come off. The first thing I notice is the poster that caused all the fuss earlier. When Fincher sees me looking at it, he says, “Daniel Craig looks like this tough guy, not realizing that the little creature standing in front of him is a far more dangerous pit bull.”

He opens a bottle of red wine, and we sit at the dining-room table, where his computer glows with eerie promise. “I think people generally don’t relish, sort of, evil fun,” he says. “They tend to think you are ghoulish if your interests run in that direction. But I don’t pretend for a moment to know what it’s really about. I know what I like about Hitchcock movies. I like that sense of uh-oooh.” He swivels around to his laptop and scrolls through a list of files on the screen, trying to decide what to show me first. We watch four or five random clips, coolly gorgeous, filled with dread, and set to a Trent Reznor score. Then he double-clicks on something and realizes that it is a rape scene and hits the stop button. “I’m not going to show you that,” he says. “That’s too heavy to drop anybody into. You gotta get there!” Scroll, scroll, double-click. “I’ll show you this,” he says. “It’s pretty heartbreaking.” It is the scene in which Salander goes to the office of her new social worker, Nils Bjurman, played with shuddersome menace by Yorick van Wageningen, and it slowly dawns on her that he is a monster who has total control over her money and her life. The scene is agonizing to watch as it slowly becomes apparent that he is going to sodomize her. Nothing is left to the imagination.

When I call van Wageningen, he brings up another difficult scene, one in which he rapes Salander. “Probably the most terrifying thing I’ve ever done,” he says. “I spent a day crying in my hotel room. I’m sure she did, too.” During the shoot, Mara said to him, “Please don’t ask me if I am OK, because I don’t want to think of you as a compassionate human being.” When I ask her how difficult shooting those scenes were, she says, “I don’t know how to describe it. I think, physically, it was hardest. I got really beat up. But I gave myself a few days and then I was fine.”

For the most part, Fincher’s films have been about the pathologies of men. In movies from Fight Club to Zodiac, he hasn’t just explored the darker side of their nature, he’s reveled in it. He even managed to make a movie about Facebook’s founder feel creepy, urgent, and disturbing. But not since he directed Sigourney Weaver in Alien3 in 1992 has his “dangerous pit bull” been a woman.

Perhaps because of this, Fincher seems a touch defensive about the choices he has made for his Salander. At dinner the night before, I used the word badass to describe Salander, and Fincher and Mara jumped all over me. “That’s a pose,” said Fincher. “It’s reductive to think of her that way. She’s not the Terminator. And you know, it’s not Dirty Harry, either. It’s way more feminine. Revenge is too easy.” Mara added, “Lisbeth lives by her own set of rules. She does the violent things she does for a reason, because it goes with her moral code.”

There is a scene in which Salander returns to Bjurman’s house knowing that she will be molested again—but videotapes it. “It’s a move on a chessboard,” says Fincher. “Somebody who is thinking in three dimensions as opposed to two. And it’s a compromise that she’s willing to make because it will free her. And then, of course, it gets worse than what anybody in the room could possibly imagine.”

In a funny way, the last time Fincher pushed these kinds of boundaries with a female character with her “own set of rules” was when he directed Madonna’s then-controversial video “Express Yourself,” in which she is portrayed as a masochist chained to a bed. How quaint that seems now. Twenty years later, he is asking way more of his actors—and his audience.

As van Wageningen says, “Let’s face it, the R-rated franchise is rebellious in itself. One morning, we were filming a sexually violent scene at 6:00 a.m. . .and I was like, ‘You want this to be the new Harry Potter?’ That scene is one of the nastiest things you will ever see on-screen. But it’s very stylish! Typical Fincher.”

“I saw this not as a blockbuster that appeals to everyone,” says Fincher. “I saw this as an interesting, specific, pervy franchise. The only chance for something like Dragon Tattoo to be made in all of its perversions is to do it big. I think The Godfather is a pretty good fucking movie. You can start with a supermarket potboiler, but it doesn’t mean you can’t aim high.”

In other words, there’s an awful lot of expectation riding on Mara’s slender shoulders. Turns out that almost wasn’t the case. Apparently, the reason for the endless auditioning process was that the studio didn’t want Mara. They thought she was too sensible, that she would never find herself in the situations Salander finds herself in. “I had said so often, ‘This is the one I want,’ ” says Fincher. “They said, ‘No. You are being obstinate. Move on.’ And I said, ‘Nope.’ Part of me wanted that last puppy that nobody else did. I didn’t want the consensus. I wanted the person that made everybody go, ‘Really?’ I needed that.”