From Goodreads:

Book #1 in the Robert Wilsop and Friends Mystery series

It's tough being fabulously wealthy Michael Stark's closest pal -- particularly when you're an underpaid copywriter for feminine hygiene products, with a lousy apartment and no lover of your own. But Robert can't resist Michael, even though the man's motto is Money Can Buy Happiness. And reformed megaslut Michael can't resist strapping southerner Max Crawford, who has agreed to marry him in a wedding that promises to be New York's ultimate gay event.
While Michael busies himself booking the First Church of Christ, Scientist, Homosexual -- and ordering enough exotic flowers to strip a tropical rainforest, Robert commiserates with Monette, who shares his envy of Michael, his affinity for practical jokes, and his inability to find a lasting same-sex love. Little do they know that what lies in store for Michael is far from wedded bliss.

The big day finds Michael, Robert, and Monette mingling with hundreds of Michael's closest friends, plus a crowd of drag queens in rustling taffeta. Curiously, the groom's husband-to-be is nowhere to be found... and neither is Michael's priceless Matisse painting.

What's a jilted lover to do? Purchase the finest rifle money can buy and vow to kill the SOB, that's what. With a reluctant Robert in tow, Michael tracks Max all the way to Provincetown, where, amidst throngs of beautiful thong-clad boys, Max turns up dead before Michael can shoot him. Primary suspects Michael and Robert swiftly go into full Hardy Boys mode, accompanied by their own personal Nancy Drew, Monette. When the clues indicate that the culprit is a murderous Bette Davis impersonator, Robert must endure the ultimate test of friendship. Does he dare go undercover with Michael in a drag revue to smoke out the real killer? Does he dare not to? Before you can say, "accessory to murder," Robert and Michael have made their drag debut in heels, sequins, and enough makeup to make Joan Collins look pasty, determined to find the real killer before the killer -- and the cops -- find them!