Ex-TV-movie-critic Tobin (Murder on the Aisle)--a jazzier hero than the author's Jack Dwyer (Murder in the Wings)--is a guest of the quiz show Celebrity Circle, taping programs on the cruise ship St. Michael, headed for the Caribbean. The idea is to up the ratings, but not by murdering the show's cast, one by one. That is what's happening aboard, however, where sweet, oversexed Cindy McBain exits a shower to find show-host Ken Norris stabbed to death on the cabin floor. Two days later the scenario is repeated with handsome, ex-series star Kevin Anderson. In between, passengers Iris Graves, a scandal-sheet reporter, and private investigator Everett Sanderson are found on deck, shot to death. Asked to help by beleaguered Captain Hackett, Tobin struggles to make sense of cryptic overheard threats, old newspaper clippings, a child's photograph, a blackmail scam, and assorted egos and adulteries--all the while pursuing Cindy, guzzling booze, and suffering the guilts about his own misbegotten life, until some ship-to-shore phone calls pay off in time to halt the carnage. The plot's barely credible, and too much time is spent exploring Tobin's self-indulgent psyche--but Gorman's breezy, unpretentious style provides some fast, forgettable diversion.