PLANNING HOMICIDE? It's a tricky business. If the ethics don't get you, the logistics will. Like two weekends ago at the Jefferson Hotel. Some pals and I tried to get away with murder -- five, to be exact. And we pulled them off. But not before some amateur gumshoes shacking up at the place nearly got the goods on us . . .

It started one clear July day when I cruised by the Source Theatre for a post-mortem on my last case. A comic thriller I'd written, name of "The Shady Side." The theater liked my work. They gave me another assignment. Something fishy at the Jefferson called "Mystery Weekend."

I got the straight dope quicker than you could say "Whose idea was this?" The hotel was an accessory in Source's scheme to mix the one's registered guests with the other's actors and stage a 36-hour live murder mystery. They needed somebody to put the pieces together. An offer I couldn't refuse.

My co-conspirator Larry Redmond and I slugged back Cokes and burned midnight oil to plan the perfect crime. We simmered and stewed till we had a nifty goulash of hidden legacies, concealed incest and secret codes.

Then I got on the trail, pawing through re'sume' files, calling actors and setting up meetings. Soon I'd found the 12 I needed -- Raoul Rizik, Pat Sheehy, Albert St. Denis, Lynn Schrichte, Laurie Spencer, Jim Hild, David Sitomer, Pauline Cottrell, Alex Takach, Michaeleen O'Neil, Bill Hollingsworth and Jim Parisi -- to play a rogues' gallery of suspects and victims.

We met on the Q-T, at discreet joints I know, to help the actors get their stories straight: director, film star, butler, widow, daughter, bastard, lawyer, housekeeper, mystery writer, astrologist, racketeer and cop. After we dished out the basic facts, they were on their own. Rehearsals rumbled late into the p.m., as characters found new motives and the plot tangled accordingly. They call it "improvisation." That's theater talk for thinking fast on your feet.

On Friday our troupe invaded the Jefferson, a ritzy little castle of a hotel more suited to the rustle of silk dressing gowns than the squeak and crack of gumshoes and gunshots. Wasn't long before we found the penguin-suited staff were no slouches at improvisation themselves. Managing director Paul Limbert and his gang hustled like old hands at the murder game, keeping track of the bona-fiders and phoney abiders while they kept the guests guessing about whodunit and who was who.

But there was one thing none of us knew about this crime business. Who were the players? We didn't have a scorecard, or a precedent. What kind of people pay for a weekend of murder? We soon found out. These guys were serious, dead set (pun intended) on unraveling the mystery and winning the game.

Friday night we tried to overwhelm them with a five-year-old murder, a fake murder, and two "real" assassinations. Stage manager Lisa Robeson and I did the legwork to make sure the right bodies fell out of the elevators and balconies at the right time. We cued the screeching entrance of D.C.'s finest and an ambulance crew who tried mightily, but unsuccessfully, to revive our first victim. Waiting to be grilled by our thespian detective, the guests drowned their tension in Bennett's lounge and got chummy.

That was our first mistake, letting them get chummy.

Saturday they started ganging up on us. As clues cropped up in their breakfasts, as they gathered for a police third-degree and toured the city on a clue-hunt ending with a bright message on the Dupont Action Lights board, it became clear they were no longer in competition with one another. It was them against us.

By Saturday night, paranoia took charge. Two more murders -- a housekeeper shot at lunch, an astrologer strangled at dinner -- and these guys got rough. For the actors, danger lurked behind every fluted column: repeated attempts to jimmy the door of a freshly deceased character's room (the actress inside overheard a would-be lock-picker ask, "Should we use the Visa or the Gold?") . . . guests listening at doors and buttonholing actors in the cocktail lounge to loosen them up for interrogation . . . a mad pillage of the hotel library for clues hidden in books . . . a daring burglary attempt by one couple, lowering themselves by bedsheet into an actor's room below. They were getting too close. The tone had shifted from Agatha Christie to Edward Albee.

Sunday morning dawned bright, and calmer. As I met with the actors for a final rundown of the denouement -- that's French for "big finish" -- the guests scurried to submit their whodunit ballots before the "dead"-line and waited eagerly for the public unmasking of the killer over brunch. The final scene went off without a hitch. The zealous crimesolvers were once again genial vacationers, responding with laughter and applause as the plot strands were tied up.

Half of the novice detectives reckoned correctly whodunit, but nobody cracked the code. They all went home patting their backs and smacking their foreheads at the same time. The actors and me? For two days we had been as suspicious as real murderers -- watching ourselves like hawks to see we didn't turn into pigeons or sitting ducks for the eagle-eyed guests. It was a monumental challenge to our craft.

That's theater lingo for "it was murder."