Credit: Robert Voets

9-10 PM · CBS · Returns Oct. 9

William Petersen has already decided that episode 10 (airing in January) of CSI‘s upcoming season will mark the end of his run as a series regular. While eager to find new challenges in theater and maybe even cable, Petersen knows his departure may not sit well with the show’s 17 million fans, especially given the high-profile exits of Jorja Fox and Gary Dourdan last season. ”We need to have new life, new blood,” says Petersen, who will retain an executive producer credit on the drama. ”It will be good for the show, and good for the writers, to have new characters. And that will be good for the audience.”

Of course, those Sin City murders don’t solve themselves, which is why the producers made it job one to recruit another marquee star to replace Petersen. Actually, make that someone who’ll follow Petersen, since no one can really replace ”the King” (Petersen’s not-so-ironic nickname on the set). ”It’s not like we’re hiring another person and calling them Gil Grissom,” explains executive producer Naren Shankar. ”I think you’re making a terrible mistake when you think of a new character in those terms. ‘We’ll make him exactly like Gil Grissom except he hates bugs!’ We’re not doing that. The new person has to be his own character.”

Since bringing back Liev Schreiber’s Michael Keppler was clearly not an option (”It’s too bad we killed him because he and I could have rotated,” quips Petersen), the producers put out feelers to John Malkovich and Kurt Russell before setting their sights on Laurence Fishburne to play a research pathologist-turned-college professor with an appetite for crime: He’s got the genetic profile of a killer! His yet-to-be-named character will join as an entry-level CSI and work with Grissom in the 9th and 10th episodes. Fishburne, who hasn’t done a regular TV gig since appearing as Cowboy Curtis in Pee-wee’s Playhouse in the late ’80s, admitted to reporters that he felt ”a little stupid and embarrassed that I hadn’t watched the show before. But the episodes they sent to me were really engaging and dark and moody, like a lot of the work I’ve been involved in.”

Lauren Lee Smith (The L Word) will also join the cast in episode 3 as a young and sarcastic CSI named Riley Adams. But perhaps the most noteworthy season 9 addition is a blast from the past. Jorja Fox — whose character, Sara Sidle, walked out on both her job and her engagement to Gil — will return, just 11 months after quitting the show, to help solve the murder of Dourdan’s Warrick Brown. ”Even though I agreed to make myself available in the future, I was surprised to be coming back so soon,” admits Fox, 40, who was vacationing in Costa Rica last March when she received the call to return to CSI. Fox knew that Petersen was negotiating his exit but had no idea that Dourdan was leaving too. ”It was definitely an ‘Are you sitting down?’ phone call. Like, ‘How many rum punches have you had?”’