A brightly promising mystery-debut with a New York theater background. Dentinger's slightly bitchy, lightly cynical heroine is Jocelyn O'Roarke--a hard-working actress now understudying the untalented Harriet Weldon in a new Broadway-bound play. (Harriet's husband, rich businessman Harold, is the prime backer.) And after the out-of-town tryout--during which Jocelyn gets the chance to give one stunning performance--the show is back in N.Y., gearing up for the opening. . . when Harriet is found dead. The top suspect? Jocelyn, of course--who had a testy confrontation with Harriet shortly before the demise. But Detective Phillip Gerrard is soon confronted with less obvious suspects and motives: Harriet's past romances with men in the cast; her homosexual son (having an affair with the set designer); etc. And amateur sleuth Jocelyn finally teams up with Gerrard to bluff out the murderer. . . and perhaps start a romance. An over-complex, just-barely-credible plot--but Dentinger's style is crisply confident, Jocelyn is fine company (warm despite her sassy veneer), and her further theater/mystery adventures might prove a welcome US answer to Simon BreWs stellar English-showbiz series.