On cue, the crane dunks the car and water comes rushing in. As she slowly sinks, Garner examines her surroundings in an almost serene near-death daze. After about 30 seconds of submersion, she stops to take a hit of air and then continues the scene. Some serious below-sea-level soul-searching ensues before she unhooks her seat belt, rolls down the window, and swims to safety--and applause. No wonder she won that Golden Globe: The girl can emote underwater!

"That was scary," Garner exclaims, descending the tank ladder. "Not fun scary, just scary." She shakes her head. "Why not put a shark in there?"

It's actually a rare moment of fear. See, Garner has been doing some out-there stuff this season--free-falling off a 50-foot cliff after being chased by barking Dobermans, crawling between buildings on a rope 90 feet in the air--while her stunt double is left sitting there thumbing through Variety. "The more risky physical stuff that she does, the more I think she feels like she's closer to who Sydney really is," observes Abrams. "Gung ho is an understatement. If anything, she's sometimes too enthusiastic. I don't think there's anything she hasn't wanted to do or done." He pauses. "There was a big explosion thing we wouldn't let her do. I'm sure she's still depressed about that."

Probably so, because there's a perfectly good reason why Garner likes to get her nice shiny hair all mussy. "Part of what's cool about the show is that it's authentic. If you look, I'm doing it," she explains. "And part of what's cool about playing this character is getting pushed in that way. So whenever it gets tough, to suddenly say, 'No, I don't want to do it'--that's not really being this girl. So I'm totally 100 percent committed to doing everything I possibly can."

Don't just take her word for it: A tour of her trailer uncovers ointments for cuts, pills for pain, kneepads and shinpads for falls, oodles of language tapes, including Portuguese, Italian, German, and Russian. To her castmates, though, it's not just the international-action-accessorized-fashion-girl stuff that distinguishes Garner. "There are times when you're acting in a scene with her, and even when the camera's on you, all of a sudden, you just kind of lose yourself in her," reports Vartan. "And you're just like, 'Oh, wow.' I don't want to make it sound like this crazy intense thing, but she just sucks you in and you can't help it. I mean, she's so beautiful but she's so vulnerable. She's just this puppy....All right, could we be any more in love with her? Seriously. Is that possible?" You would think not, but wait...

The biggest test of Jennifer Garner's espionage skills was not swiping Russian computer files or disarming a nuclear bomb or even crushing the thorax of her crazed Taiwanese torturer while cuffed to a chair. No, Garner's most impressive stunt went down right here inside Alias HQ. "One night, I finished work and I went into the [production] offices to look for J.J.," shares Garner. "So I'm walking by and I notice that the door to the writers' office is ajar. It's strange, because we've never been invited in there. There's this huge bulletin board with index cards with ideas for what's going to happen to each character in each episode. And I went in and I read every single one of those index cards.