CSI executive producer Carol Mendelsohn has confirmed exclusively to Entertainment Weekly’s Michael Ausiello that William Petersen (Gil Grissom) will be gone by midseason! And not “off too do a play” gone like he was back in 2006. No, this season’s 10th episode will be his last as a full-time series regular.

“Billy is leaving,” confirms the show’s executive producer, Carol Mendelsohn. “But he will remain throughout the run of the series an executive producer. And he will, whenever CBS asks, come back. I don’t think you’ve seen the last of Gil Grissom.”

Neither does Petersen. In fact, in an exclusive interview conducted last Friday, the eight-year CSI vet seemed almost reluctant to characterize his departure as, um, a departure. Citing both his ongoing role as an executive producer AND his intention to return on occasion as a (very special) guest star, he said, “I’m in a great place in terms of knowing that I’ll be more free to make choices. And I’m responsible enough to not do it in a way that would hurt [the show].

“I want it to work for the writers, I want it to work for the cast, and, MOST importantly, I want it to work for the audience,” he added. “I don’t want them to abandon the show.”

In the meantime, Mendelsohn is plotting one hell of a send-off for her leading man. The events of last season’s finale — specifically the death of Gary Dourdan’s Warrick — will push Grissom to the breaking point. “The easiest way to describe Grissom is ‘in crisis,’” Petersen told me. “As a man. As a scientist. As a teacher. As a middle-aged person who has been very successful at what he’s done… [he] wonders, ‘What’s the point?”

Helping Grissom through the crisis will be his true love, Sara, played by Jorja Fox, who is returning for multiple episodes, starting with the season premiere. “I wouldn’t want to say exactly what we’re going do — I want people to watch, certainly,” he chuckled. “But Sara is involved… It’s often darkest just before the dawn.”

And lest anyone read any hidden meaning into that statement, the actor reiterated, “For me, it’s a really good situation. I don’t want the audience to think it’s NOT… [It isn't] like there’s something going on, like ‘Petersen’s unhappy,’ ’cause it’s not true. It’s quite the contrary. ”

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