Lena Olin's Irina may not be returning to Alias anytime soon, but Sydney's spy family will remain relatively dangerous. EW has learned that Isabella Rossellini will guest-star in a couple of episodes as Katya, a lethal ex -- KGB agent who's been working underground with...her sister, Irina! (In the Jan. 18 episode, Katya is enlisted by Jack to help rescue Syd and Vaughn from a North Korean firing squad.) ''Obviously she's beautiful, but she's got this wonderfully mysterious presence,'' says series creator J.J. Abrams of the Blue Velvet star. ''She just felt like she would totally fit into the Alias universe.'' The 51-year-old Rossellini hopes her ass-kicking and name-taking skills are up to snuff: ''J.J. said, 'Are you athletic?' and I said, 'Well, I don't know, I do some yoga, some Pilates.' So I might be in for a big surprise. I am getting a little bit on the side of a little old lady, but I'm sure that J.J.'s going to make me look like Uma Thurman in Kill Bill, so why not, no?''