Agatha Christie's writing career spanned about 50 years, but her play, "The Mousetrap," which opens Friday at Butler Little Theatre, has been on stage even longer.

The murder mystery, about a dwindling group of guests trapped in a English inn during a storm, has been continuously performed in London's West End for 55 years.

The enduring popularity of the play constitutes something of a mystery, as well -- one that may yield its secrets only after close interrogation of some of those involved in Butler's production.

Upon questioning, director Sam Minehart, who has been a frequent actor, director and producer at Butler Little Theatre and also serves as publicity director, admitted that the theater's play-reading committee chose "The Mousetrap" because of the author's popularity and because their audiences enjoy mysteries.

"We usually do a mystery every season or two," said Ms. Minehart. Her voice, which can also be heard in local radio and television spots, gave nothing away.

"It's a puzzle," she said of the play. "At any time you can suspect any one of the characters. You have to listen carefully to what they say."

Good advice, but the plot only thickened when Tom Dillon, who plays Detective Sergeant Trotter, denied having much acting experience despite having a central role in the production. Mr. Dillon noted that he has stage experience, just not as an actor.

"I've been in a metal band for years called 'Yigga Digga,' " he said. "But they haven't done as much performing lately, so I got an itch to be involved in something like this."

Mr. Dillon admitted that he is enjoying the process of taking on another identity and said he took on a cockney accent, too.

"The Beatles taught me that," he said. "Well, and the Geico gecko."

Attention turned to frequent Butler actress Katy Steele. What part does she play in the mystery? A smaller one, it turns out, as her character Miss Casewell often stays in the background.

But she noted cryptically, "In a Christie play, all the parts are important." Sis Fleming and Dan McCarty play innkeepers Mollie and Giles Ralston. Jeff Carey, who just starred in the theater's "Same Time Next Year," performs as Christopher Wren, and Sue Switzer is Mrs. Boyle. Dean Weiland is Major Metcalfe, and Federico Scasso plays Mr. Paravicini.

The answer to why Agatha Christie's "The Mousetrap" has endured for more than half a century seems destined to stay shrouded in secrecy, but perhaps Ms. Steele said it best:

"There's a reason she's called the Queen of Mystery."

"The Mousetrap" will be performed at 8:15 p.m. Friday, Saturday and March 14 and 15; 7:30 p.m. March 11, 12 and 13; and 2:30 p.m. next Sunday at Butler Little Theatre, 1 Howard St., Butler. Tickets are $10. Call 724-287-6781.