"I'm very much invested in `The Bug Man'," Fishburne said of his affection for Petersen's Gil Grissom, an entomologist who heads up the CSI investigative team, but who is now leaving.
"I mean, really, they can't kill `The Bug Man'! Being a fan, I don't know how I'm going to feel when the new guy shows up."
By the way, the "new guy" is Fishburne.
The square-jawed actor, whose authoritative voice and distinctive features have made him a formidable force on the big screen (The Matrix franchise and his Oscar-nominated performance as Ike Turner in What's Love Got to Do With It) and the small screen (Miss Evers' Boys) and stage (a 1992 Tony Award in Two Trains Running) for almost three decades is making his most unusual career move: joining the cast of the top-rated CSI as criminal pathologist Dr Raymond Langston.
CSI producers say Fishburne was their first choice for Langston, who will be introduced on Thursday in the first of a two-part installment in which Grissom abruptly announces that he's leaving the unit.
Petersen's last episode is on January 15, in which Langston officially joins the CSI scientific forensics team as a lower-level investigator.
Fishburne said he's excited and energised by his new project, adding that hooking on to a hit TV drama while he's still active in film and theatre makes sense at this point in his career.
"I've tried to approach this with an open mind - and a great deal of humility as well," Fishburne said, his closely cropped hair speckled with grey.
"And I'm not fooling myself - I am filling the shoes of a man who is irreplaceable. Once I recognised that, then I knew exactly what my responsibility was. My purpose is to serve the show.
"That's one of the most important things to remember. This is not about me. This is about the audience."
And although work has been pretty regular since his first notable role, as the bean pole-thin soldier in 1979's Apocalypse Now, he said the weekly schedule of CSI will allow him to spend more time with his family - wife Gina Torres (24, Alias) and their 18-month-old daughter.
"This comes at the perfect time in my life," Fishburne said.
"I had always thought I would do something like this when I got to be 50 - and I'm 47 now."
The transition to television - and the ensemble CSI cast - has been smooth.
"The good news is that in the last six weeks, the focus has really been on Billy. So that has let me just quietly observe, showing up for work and trying to integrate myself as harmoniously as possible. And everybody could not have been nicer."
He's also figuring out his new character: "I'm in the process of discovering who he is. It's a continual process.
"All I know is that I bring a certain gravity and weight to the series, and the writers and producers have carefully constructed a character that allows me to play to my strengths."
Fishburne, who has a contract to stay with the show for 1 1/2 seasons, receives an entrance worthy of a star.
Though Langston is a professor, his character still has a sense for the theatrical.
When he is first seen, he's in the shadows, preparing to conduct a class that will feature an interview via satellite with a serial killer (Bill Irwin). (Grissom sneaks into the lecture.) As he begins, a light illuminates Fishburne's face.
Co-executive producer Carol Mendelsohn said Fishburne's introduction was carefully mapped out.
"A tremendous amount of thought went into that. We wanted our audience to have the same kind of anticipation of this guy that Grissom has. He's a man of magnetism and power who is leading the class into a very dark place."
Co-executive producer Naren Shankar said Fishburne was at the top of their wish list: "We proposed the kind of character he had never played before.
We dropped a ton of DVDs on him, and he said he wanted to do this. It was such great encouragement to attract an actor of his calibre."
Fans of CSI should not expect dramatic changes in the show's format or structure.
"The DNA of the show will remain the same," Shankar said. "Billy Petersen had always said this show is about people doing their job. Laurence will bring a new dimension and vibe to it."
