Hayden Danziger is on a cruise with his wife Sylvia, who is older than he and much, much richer. Rosanna Wells is on the same ship as a singer. Rosanna and Hayden are lovers and Rosanna blackmails Hayden, but he has decided to kill her and has planned the perfect crime. Or so it seems since Lt. Columbo is cruising on that same very ship and the Captain asks for his help.