During an argument with his wife at home, Hugh Caldwell accidentally kills her. Not knowing what to do, he turns for help to his friend and neighbour, Deputy Police Commissioner Mark Halperin. Halperin agrees to help Caldwell by breaking into his house while Caldwell is in a bar and setting up the scene to make it look like Caldwell's wife was killed by a jewel thief who has done several jobs in the neighbourhood.
Halperin's help comes at a cost, however, since he wants his wife's millions and murders her by drowning her in the bathtub. Halperin blackmails Caldwell into posing as the jewel thief and throwing his wife's body into Halperin's pool to make it look like this second murder is also a jewel theft gone wrong.
Although Halperin's plan has several subtle flaws, his biggest mistake is assigning Columbo to investigate the case. Columbo is undaunted by the prospect of accusing his own boss of murder and enlists the help of the real jewel thief to prove Halperin's guilt.