On the Burbank, Calif., set of Alias, a recently rescued prisoner is quietly recounting details of unthinkable torture.

Her eyes are hollow with exhaustion. Scars and bruises form grotesque ribbons around both wrists. But while series superspy Sydney Bristow, played by Jennifer Garner, has witnessed this scenario countless times before, she can't help but fight back tears. After all, the broken beauty before her is her mother, Irina Derevko, and until moments ago, Sydney believed she had been offed by her pops (Victor Garber).

"But no one really dies on Alias, right?" asks Lena Olin, who's returning as the duplicitous Derevko after a two-year absence from the ABC spy serial. "I am definitely back."

And how. Irina may not be, as creator J.J. Abrams cracks, "resurrected from the dead with some kind of Rambaldi serum," but her return will provide a shot of adrenaline to the end of the season. In the May 18 episode, Sydney and Co. discover that Irina is being held captive by her power-hungry sister Elena (Sonia Braga); they break her out, just in time to help (or hurt?) Sydney as she tries to prevent a Rambaldi-foretold apocalypse in the May 25 finale. (Syd will have a bit of bliss when Vaughn, played by Michael Vartan, suddenly pops the question.) "It's a wild finale," Abrams says excitedly. "And in order to make it work the way we wanted it to, we needed Lena."

Abrams had been trying to lure the 50-year-old Swedish-born actress back since she abruptly left the drama in May 2003. Rumor had it that money was the sticking point, but Olin claims her reasons were strictly personal. She says she had always intended to leave Alias when her contract was up in order to spend more time with her New York-based family, which includes film-director husband Lasse Hallström (The Cider House Rules), teenage son August and daughter Tora, 9. "I had been away too much," says Olin, "and I needed to stay at home for awhile."

She took her daughter to school in the mornings and contemplated moving the family back to Sweden. Occasionally, she slipped off to make a movie, most notably the upcoming Casanova, directed by her husband and starring Heath Ledger. Olin admits that for some time she refused to take Abrams' calls. "When I talk to J.J., it's really hard to say no," she says with a laugh. "I knew if I talked to him, he'd be able to convince me to come back."

That was the case when they finally spoke earlier this year. "Time had passed," says Olin, who's open to returning next season. "I was like, 'Let's do it.' And it's been so fun."