When he started out as an actor, Sean Murray knew he was launching a career that usually doesn't have much in the way of job security. As it turned out, he's been playing Timothy McGee for 18 seasons on the CBS drama "NCIS."

"In this business, especially as an actor, that just does not happen very often," Murray said. "Shows are not meant to go that long usually, so it is definitely a unique position to do one character and one job for 18 years. It's wild."

But it wouldn't have happened had the character not evolved. "We had those conversations right at the beginning," he said. "McGee started out as this rookie agent, but I remember saying, 'I don't want it to be like baby Maggie Simpson where every week you revert to the same character; there has to be growth.' And I think that McGee has probably changed over time more so than any of the other characters on the show."

McGee is a computer nerd. Murray is something of a computer nerd himself, he admitted, which makes it easy to deal with all the techie jargon. But it doesn't always work out quite as neatly as he would hope.

"There was an episode where I had mountains of dialogue in every scene," he recalled. "And the pace of shooting television is just go, go, go, go. As soon as you finish a scene, you have to be ready to go on the next one, and it might be four pages of dialogue."

Brain overload

"I was doing a scene with Pauley Perrette in Abby's lab, and I had a monologue. And because of all the dialogue memorization I had done for this episode, my brain just hit a wall. I remember feeling panicked and looking at Pauley after rehearsal and saying, 'I'm not going to remember a word of this. I can't do this.'

"Pauley said, 'Sean, we've all had that happen. Here's what I want you to do: I want you to take a piece of paper and write your monologue down, and I want you to stick it on the computer in front of you and I want you to read it as if you're saying it to me.' "

He initially refused, responding that it wasn't professional. "But it became a matter of pure survival; you're there to get things done," he said. "So I did it [laughs]. I wrote down the monologue and I stuck it to the computer and I read the entire thing during the scene, and I felt like the worst actor in the world."

It wasn't the first time he'd had to fake it. When he was starting his career, he got a role in 1992 in the TV series "Civil Wars" in which he played a tennis pro.

"The shot was set up so that I was supposed to just serve the ball, and the other guy would miss it," he said. "We tried to do it about eight times, and I couldn't get it over the net. The whole thing was so bad that they ended up having someone throw the ball over the net from off camera, and then I ran in like I had just hit the ball."

Living with the memory of that embarrassment, it was hard for Murray to watch the "NCIS" episode in question.

"I was so scared because I knew the scene was coming up, and I was so nervous to see what was going to happen," he said. "And none of it looked fake in any way! I was like, 'Wow, I guess I pulled it off.' "