A first mystery, set in Lenox, Mass., from former Wall Streeter Goldstone (Trading Up, 1988; the thriller Bad Business, 1991). Here, Elizabeth Halprin, mother of 11-month-old Emily, is nearing final divorce, after a three-week marriage, from self- seeking, womanizing Howard Hack, writer of boring books. Howard's pre-separation affair was with rich, chic, man-eating author Margaux Chase, who introduced him to agent Francine Weezle and publisher Phillip Laramee. Now they're pushing Howard's Passion Palace to best-sellerdom, even though Margaux is history and Howard's new squeeze is novelist Holly Ivy. All these people and a hundred more, including Elizabeth, are guests at a Halloween party at Margaux's mansion. Elizabeth leaves early, and so the next day before she learns that Howard's naked body, shot through the head, was found in one of the mansion's bedrooms. She also discovers that, with the divorce still unfinalized and Howard's will unchanged, she's heir to his considerable fortune, making her the number-one suspect. With help from other playground momslawyer Pat; computer whiz Astrid; general organizer DidiElizabeth gets off the hook, and on her own cracks the case. Lots of chirpy conversationa great deal of it directed, in monologues, at hapless Emily. But the blithe plotting lapses into sheer silliness as it arrives at its far-fetched, unconvincing conclusion. Mildly diverting.