Forget Cats and Les Misérables. Who would have thought that one of the longest running and most popular plays in America would be the quirky interactive comedy Shear Madness, the sleeper hit that woke up as a phenomenon. From Washington DC to Chicago to San Francisco, this whodunit has conquered the national theater landscape city by city with a sleek brand of topical, offbeat humor that asks the audience members themselves to solve the night's farcical caper, set in a unisex hair salon.

This success is most evident in Boston, where the current production of Shear Madness is celebrating its 20th birthday. This laugh-riot locomotive seems to have enough fuel to steam on for another 20 years; Beantown theatergoers keep coming back for another trip. Shear Madness invaded the 199-seat Charles Playhouse Stage II in 1980, and has become such a popular fixture that its address - 74 Warrenton Alley - has been renamed Shear Madness Alley.

The comedy revolves around an introverted concert pianist who is murdered above a unisex barbershop. It's up to the detective and the audience to deduce which of six suspects is the murderer. Was it Barbara, the tough-as-nails hairdresser? Tony, a fabulously gay barber? Or Eddie, an antique dealer? The crime unfolds over the course of two acts and, after the intermission, the detective quizzes the audience, encouraging them to blurt out comments and grill the suspects. The ending is different each night, depending upon the reactions of the actors to the audience's queries. But it's not required that everyone participate; you can act the armchair Hercule Poirot or just sit back and enjoy the laughs. This unpredictable formula, coupled with casts comprised of top local comic talent, is what keeps people returning for more. Shear Madness is the perfect hair tonic for a wrinkled brow.

The show is based on a serious psychological titled Scherenschnitt, written in 1963 by German playwright Paul Pörtner. Marilyn Abrams and Bruce Jordan believed that the dour mystery was a comedy screaming to get out; so they acquired all the rights, adapted it, and turned it into a groundbreaking romp. Not only a commercial success, Shear Madness has won a multitude of awards, including seven Boston Globe Awards for Best Comedy of the Year. The show has also been acknowledged by the Guinness Book of World Records as the longest running non-musical play in American theater history. It looks like it's poised for further success--proving that, for your hard earned two bits, you can always get a shave, a haircut, and a belly laugh at Shear Madness.