The confetti has just settled at The Charles Playhouse following the 30th-anniversary celebration for "Shear Madness." Set in present-day Boston, "Shear Madness" is all about the scissor-stabbing murder of a famous concert pianist who lives above a unisex hair salon on Newbury Street.

Having played to more than 1.8 million people since opening at The Charles in 1980, the interactive comedy-whodunit holds the Guinness record as the longest running play in the history of the American theater. The twist is that the audience helps solve the crime every night, making each performance a little different. As well, the show is constantly updated with topical references and jokes, many of them based on that day's headlines.

At the center of the mayhem is leading man Patrick Shea. Playing Tony Whitcomb, the owner of the salon, Shea gives an over-the-top performance that delights audiences night after night. He joined the cast in 1983 and has been appearing in the show, in his words, "more on than off" ever since.

Originally from New York, Shea was raised on Boston's North Shore. In addition to eight shows a week for “Shear Madness,” he has also found time to serve as narrator at several Boston Pops concerts, double for David Letterman and appear in such feature films as "Gone Baby Gone," "Mystic River" and Ricky Gervais's "The Invention of Lying."

We spoke on the morning of a busy two-show Saturday. Here's an edited transcript of our conversation.

BIR: An actor's life is known for being transient. Performers are always in search of their next job. For you, "Shear Madness" has been the exception to the rule.

PS: Yeah, I've been very fortunate. "Shear Madness" actors are always looking for another gig. Not that we don't love doing "Shear Madness," but it's good for the show for actors to get out and do other shows. Or do other projects and then be able to come back with renewed energy and renewed good humor and better skills. It's terrific to be able to have such longevity in a show and to know that it's going to be there for you.

BIR: "Shear Madness" gets a tremendous amount of repeat business.

PS: I've run into people at the theater who'll tell me during the break or after the show, "We've seen the show 14 times. Every time we have relatives coming in from out of town, we bring them in because it's really a slice of Boston life."

BIR: "Shear Madness" is also known for it's topical humor. That has to keep the cast on its toes.

PS: Some of the best actors in town have done the show over the years . . . The ones who are so good are the ones who bring something to it every day. They read the newspapers. They always have ideas. And they're thinking about keeping the show as current as possible.

BIR: What's the process for adding fresh material and new jokes.

PS: I tell you, the process is We Never Know. We kind of hash things over before the show. . . Most of us get there about an hour before show time. We look at the newspaper and talk about news stories, just conversationally, and then we'll come up with something that might fit into the show. Sometimes, somebody who's not even in the show at the moment will call up and have a great idea. That always amuses me . . . They might be doing a show somewhere else in the country, and they'll call up and say "Hey, I got a great idea for a joke." (Laughing.) Part of me wants to say, "Hey, get a life."

BIR: Tell me how you originally came to the Boston area.

PS: My father's family is from New York and my mother's family is from Salem. But my Dad died when I was really young, I was only three years old when he passed away, so my mother moved back to Salem. I went to school in Marblehead, Swampscott, and Salem. I spent most of my life growing up in Salem. The Sheas are from Kerry, and the Deerys, which is my mother's family, are from Roscommon. My grandfather was a New York City cop. He worked his way up to being a Precinct Captain.

BIR: Any history of show business in your family?

PS: My mother's father owned movie theaters in Salem -- The Empire and the Paramount, and one other one, The Federal, which was torn down long before I was born, I think.

BIR: Your physical appearance got you a job playing David Letterman's double. How did that happen?

PS: That was strange. I do a lot of corporate work -- trade show and videos. I was doing a job for MetLife and a guy that works there . . . was asked if they knew anybody who did Letterman . . . He put me in touch with this agent in New York . . . and the agent had me go down and interview. They took a look at me and said, 'Well this guy looks a lot like Dave.' (Laughs.) So I did about a half dozen of those and it was really fun. They sent me out to Indiana to bring flowers to his mother on Mother's Day. I spent the whole day with his mother and his sister -- really nice people. On the live broadcast, Dave said, "Mom, I'm sorry I couldn't be there with you on Mother's Day, but here's a guy who kind of looks like me."

BIR: I've also heard you on Irrational Public Radio as Zoldar, Venutian Prince of War (irrationalpublicradio.com). The humor in that show is so spot-on.

PS: (Laughing.) That's Joe Smith, another "Shear Madness" alumnus, who created that. It's very funny, don't you think. That was my "Robert Siegel."

BIR: You've also had a nice connection with The Boston Pops.

PS: Dennis Alves at the Pops had been looking for someone to narrate and play all these roles in "Carousel." I'm not exactly sure, but Will LeBow may have recommended me. Dennis had just been to see "Shear Madness" the week before, and he said, "Oh, I know who that guy is." "Shear Madness" does actually breed a lot of work. It's amazing how many different kinds of people come and see this show. So that was the first gig that I did with the Pops and then it kind of blossomed from there. Keith [Lockhart] has been very nice and asked me to come back and do "Polar Express" and then I did the Aaron Copland piece ["Lincoln Portrait"] as well. I hadn't been to the Pops since I was 14 years old. And the next thing I knew, here I am, a big grown up, sitting on stage right next to Keith. It was just great.

"Shear Madness" continues at The Charles Playhouse, 74 Warrenton Street, in Boston. For information and tickets: 617-426-5225. shearmadness.com