There hadn't been a murder in the picturesque coastal town of Castine, Maine for 100 years. But this one came as no surprise, since it was part of Captain Morgan's Mysterious Manors mystery weekend, plotted by Dave Landau. As president of Murder To Go, Landau, 27, goes around putting together whodunit parties and has committed "murder" aboard trains and ships, in hotels and even in private homes.

Present for the killing in Castine were 35 people who paid $275 apiece and came from as far away as Florida to test their Sleuthing skills. The case revolved around a mythical buried treasure, supposedly hidden 300 years ago by the pirate Henry Morgan. A lengthy poem, written by Morgan and riddled with clues to the treasure site, was read aloud on the first night. Mingling with the paying guests were a handful of professional actors, planted by Landau to drop red herrings and act suspiciously.

Before the murder, guests found a crumpled note. "We kan find the tresu together," it read. "Meet me at the towne dok at midnite." It was signed "X". By the time the gunshots were heard, everyone was beginning to suspect one another. Next morning at breakfast, conversation buzzed over the discovery of blood on the inn's back steps. One guest was overheard saying, "We should have done him in 10 years ago," while two others were seen sneaking up the stairs.

A few hours later, when most of the guests had been lured away for a walk, a neighbor spotted the body of Steven Porter (in reality a college student recruited by Landau). When the guests returned, an ambulance and police car were in the driveway and Detective Peter J. Lyric was waiting to question them. The young, curly-haired detective was quickly sized up as an actor and evoked grins and giggles from the guests as he began his interrogation. "Who's stayng in Room 3?" Lyric asked. Bill and Jody Multack from Miami responded. "Porter was found on your balcony," snapped Lyric. "Do you know anything about this?" They pleaded innocence. Accusations and denials flew. "This is a real madhouse," the detective grumbled.

After Lyric left, the guests gathered in small groups, exchanging possible murder motives and trying to unravel the clues that would lead them to the treasure. Then, at 4 o'clock, came a startling development. Phil Webster, another so-called guest, was shot and killed inside the Unitarian Church.

But let's start, as they say on those cop shows, at the beginning. Landau's entry into the whodunit business is no mystery. A distaste for parties and fond memories of playing Clue as a child triggered his mock-murder concept. He began running mysteries on trains, later expanding to corporate functions and private parties. He charges companies $3,000 per mystery. To create an aura of authenticity he weaves local history into his plots, draws up floor plans and arrives early to rehearse actors.

Pretending to be a guest, Landau never reveals his identity, allowing himself to direct the flow of events discreetly. By now he's learned that nothing ever goes completely according to plan. In Castine one craft guest actually witnessed the first murder, and a broken third-floor window caused a hasty script revision. "It takes a lot of thinking on your feet," admits Landau.

Landau grew up in Allentown, Pa., where his father was a college math professor and his mother a community volunteer. After studying filmmaking at Ithaca College, he moved to New York City in 1978 and began working as a movie electrician. He later began penning mystery stories and is a member of the Mystery Writers of America. Nowadays he plots his capers in his small Greenwich Village apartment.

The resolution of the Castine mystery came at a party held late Saturday night, where guests turned in ballots marked with their whodunit picks. Earlier the treasure chest had been uncovered on the beach but remained unopened. Upon Detective Lyric's arrival, its contents were revealed, creating a wail of protest and a flurry of activity. A scuffle ensued and a gun was drawn. A few seconds later the murderer was caught while trying to escape. (Sorry, his identity must remain a secret.) Landau gave the 15 guests who solved the murder phony gold doubloons for their sleuthing skills. Case closed. Weekend over.

TOBY KAHN