Although Isabel Czerny has died more than 6,000 times during the run of ''Shear Madness,'' the play enjoys the distinction of being the longest-lived nonmusical in American theater history.
Last week, the Boston whodunit, an audience-participation comedy set in a sociable unisex hairstyling salon on Newbury Street, marked its 15th anniversary at the Charles Playhouse. The regular cast of a dramatic hairdresser (Patrick Shea), his trendy assistant (Paula Langton), a Boston socialite (Ingrid Sonnichsen), a shady antique dealer (Richard Snee), and two detectives was joined by several real-life local experts in law and criminology. These included prominent lawyers Joseph Balliro Sr., Arthur R. Miller, James Sokolove, and Jack Zalkind to defend the hair-salon suspects in Czerny's murder.
While many artistic ventures have tended toward lavish productions with sky-high budgets, ''Shear Madness'' has struck on quite a different formula for enduring success. The stage, while invitingly framed with cheery yellow wallpaper and set with familiar salon supplies, is small and rather simple; the plot, though engaging, is an age-old story; and the acting, while polished after hundreds of performances, does not require delicate nuances of character.
Yet this is all part of the charm of ''Shear Madness.'' The show plays up its low-key atmosphere with a relaxing cabaret setup, and the action begins onstage as the audience is still filtering in.
The plot quickly thickens, as a number of suspicious movements by salon occupants result in Czerny's murder in an upstairs apartment. The detectives, who were already on the scene, grill the four suspects separately.
And then, as the houselights come up, the madness begins. The detectives call upon the audience as witnesses to the grisly doings.
After verifying the exact sequence of events with the witnesses, the detectives invite them to ask the suspects questions -- eventually the audience will vote on who committed the murder.
On this night, the guest lawyers, who were sitting in the front row, rushed to the defense of their ''clients.'' Their high-flown speeches poked fun at the profession and spoofed several current court cases.
The spontaneity particularly apparent on the 15th-anniversary night of ''Shear Madness'' has factored strongly in the play's success. The audience responded most strongly to the improvisational jokes prompted by audience comments, with one of the night's biggest laughs coming from a quip about a spectator's ''tragic'' haircut. And even the regular cast members couldn't hide their laughter at the surprises en gineered by the guest performers.
''Shear Madness'' has tailored performances to other locales, too, as producers Marilyn Abrams and Bruce Jordan have created sister productions in as many as 22 other cities -- including Chicago, Washington, and even Rome and Tel Aviv. Some of the shows in these locations have come and gone, but Boston's has remained strong since its pioneering performance on Jan. 29, 1980.
The play's appeal may be heightened further by the media's current attention to several sensational murder trials; the play may even encourage thought about the legal system.
When the audience was called upon to verify what transpired in the hair salon, for example, a variety of conflicting accounts surfaced. And if audience members can't clearly recall events from a half-hour ago that they keenly observed, it makes one wonder how witnesses to actual crimes can be relied upon to testify accurately.
But ''Shear Madness'' is not about answering such weighty questions. Its aim is to uncover the culprit in the most entertaining way.