All together now, CSI fans: Breathe. Executive producer Carol Mendelsohn assures me that her team was anything but blindsided by the upcoming departure of William Petersen. “We do have a plan,” she says. And that plan includes not only Grissom’s sure-to-be-stellar swan song, but also the arrival of some new blood (one with funky DNA), the return of some old blood (welcome back, Jorja Fox!) and an episode that’s been nearly nine years in the making. Here, Mendelsohn and fellow EP Naren Shankar offer an exclusive preview of what will go down when this sure-to-be-controversial season starts up.

* Jorja Fox will be back for “multiple” episodes, beginning with September’s season premiere — an hour that will also feature an appearance by Gary Dourdan’s Warrick, who was seemingly shot to death in last May’s finale. “We’re not saying whether or not Warrick lives or dies,” hedges Mendelsohn, “but we will say that the premiere may be the last time our loyal fans see the entire original CSI cast together.”

* Previously-announced addition Lauren Lee Smith (The L Word) joins the cast in the third episode as new CSI Riley Adams. “She will come in to ostensibly replace Sara Sidle,” says Mendelsohn. “She has a very distinct personality… a very wry sense of humor. She doesn’t take herself too seriously.” Adds Shankar: “This is a person who, unlike the rest of our gang, has not had Grissom as a mentor. So there’s a very different relationship between Riley and Grissom.”

* Another new CSI, this time a male, will be brought in later this fall, but “he will not appear on the landscape as a CSI to begin with,” teases Mendelsohn. “He’s a professor with background in pathology. He will appear when Grissom is investigating what will be a two-part case. He will help Grissom and the team bring the perpetrator to justice, and then this character will stay around and ultimately become a CSI.” And although Mendelsohn says the new guy (who will possess a very rare genetic abnormality) will “not necessarily [replace Grissom as] supervisor,” he’ll inevitably be branded Petersen’s replacement — if for no other reason than the caliber of actor being sought for the role: Kurt Russell, Laurence Fishburne and John Malkovich are said to be at the top of CBS’ wish list. Of the three, Mendelsohn would only confirm that Malkovich was approached, adding that “scheduling conflicts” had quickly taken him out of the running.

* Current cast members Liz Vassey (lab rat Wendy) and David Berman (coroner David) have been upped to full-fledged series regulars. Wallace Langham’s Hodges, meanwhile, will become more prominent.

* Arguably the drama’s most infamous serial menace to date, the Miniature Killer, “will come back for an episode,” Mendelsohn reveals. “Grissom will cross paths with her.”

* Finally, the show will celebrate its landmark 200th episode this spring with a blockbuster installment helmed once again by Petersen’s good friend (and To Live and Die in L.A. director) William Friedkin. Is it fair to assume that this could be the episode in which Petersen debuts as a very special CSI guest star? “Billy will definitely be on the set for Mr. Friedkin’s episode — whether it’s behind the camera or in front of the camera is TBD,” Mendelsohn teases. “I don’t think you’ll be able to keep him away once he’s back in L.A.”

Wait, there’s more — but you have to pick up this week’s issue of Entertainment Weekly to find out what other cool surprise CSI has in store for you this season. That’s on sale this Friday, but there’s plenty to do in the meantime. For starters, you could start filling up the comments section with your thoughts on CSI: TNG. Will these new characters fill the void left by Petersen, Fox and Dourdan? Can they? Are you sticking with CSI for the long haul? Or are you now thinking of playing the field Thursdays at 9? Discuss below!