EW's TV scooper dishes on William Petersen's departure from ''CSI''

Turns out there was a time bomb buried in the new CSI contract William Petersen signed last March: This season’s 10th episode will be his last as a regular. ”Billy is leaving,” confirms executive producer Carol Mendelsohn. ”But I don’t think you’ve seen the last of Gil Grissom.”

Neither does Petersen. In fact, he’s reluctant to even characterize his departure as, um, a departure. ”I’m going to stay as involved as I’m allowed to be,” says the actor, who will remain an exec producer and intends to return as a guest star on occasion. ”And I’m responsible enough to not do it in a way that would hurt the show.”

CBS has to be concerned about that too. Although no one expects the series’ post-Petersen ratings to nosedive, the network’s top-rated program is facing a huge challenge. His swan song, coupled with Jorja Fox’s and Gary Dourdan’s recent exits, means that three original cast members will have left in a year. ”This will be a year of transition,” concedes Mendelsohn, who’s confident that, like Law & Order and ER, CSI can weather such cast shifts. ”But we are not out to just replace those actors. We’re out to add new characters, and the show will change as a result.”

In the meantime, Mendelsohn is plotting one hell of a send-off for her leading man. Just as this will be a year of transition for CSI, so too will it be for Grissom. ”The easiest way to describe him is ‘in crisis,”’ Petersen says. ”As a man. As a scientist. As a teacher.” And don’t forget lover. Not only will Grissom’s longtime temptress, Lady Heather (Melinda Clarke), reappear, but so will his true love, Sara: Fox will return for multiple episodes. ”I wouldn’t want to say exactly what we’re going to do,” says Petersen, teasing fans who hope Sara and Grissom will ride off into the desert together. ”But she is involved.”

The Post-Petersen Plan

Grissom may be turning in his lab coat, but the show must go on. And judging by the evidence put forth by CSI boss Carol Mendelsohn, things look promising. Among the highlights of CSI 2.0:

· Previously announced addition Lauren Lee Smith (The L Word) pops up in the third episode ”to ostensibly replace Sara,” says Mendelsohn. ”She has a very wry sense of humor [and] doesn’t take herself too seriously.”

· Another new CSI, a male professor with a genetic quirk, will be brought in later this fall. Although Mendelsohn says he ”won’t necessarily [succeed Grissom as] supervisor,” he’ll inevitably be branded Petersen’s replacement — if for no other reason than the caliber of acting being sough for the role: Kurt Russell, John Malkovich, and Laurence Fishburne are said to be at the top of CBS’ shortlist.

· Recurring cast members Liz Vassey (lab rat Wendy) and David Berman (coroner David) have been upped to full-fledged regulars, while Wallace Langham’s Hodges will be featured more prominently.

· The show will celebrate its 200th episode this spring by bringing back Petersen’s good friend (and To Live and Die in L.A. director) William Friedkin to helm. Might this be the episode in which Petersen makes his debut as a very special CSI guest star? ”Billy will definitely be on the set for Mr. Friedkin’s episode,” Mendelsohn says. ”Whether it’s behind the camera or in front of the camera is TBD.”

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