Gat Heat — Richard S. Prather

When his client turns up dead and naked, Shell Scott focuses on the widow
 
Everyone at the party is naked. It's just that kind of scene. Even the corpse seems to have forgotten his clothes. Private detective Shell Scott has tangled with the toughest 'hoods in Los Angeles -- and has the scars to show for it -- but even he isn't prepared for a gathering of Southern California's most murderous nudists. He's been summoned to the party by the host, George Halstead, on a matter of “peculiar delicacy,” but he'll soon discover there's much more to this mystery than a single unclothed stiff.
 
As it turns out, it's Halstead who's both naked and dead, and his widow is eager for Scott to crack the case. Before he knows what hit him, this PI will be neck-deep in blackmail, murder, and enough bare bodies to fill the grotto at the Playboy Mansion.

Gat Heat is the 33rd book in the Shell Scott Mysteries, but you may enjoy reading the series in any order.