Ruth Lytton and her brother Edward are the curator and trustee, respectively, of a museum bequeathed to them by their mother. The museum is in dire financial straits, so Edward wants to sell it before it falls even more deeply in debt. To make matters worse, Ruth's niece Janie Brandt has hired the good-for-nothing brother Milton of her lover Dr. Tim Shaeffer as the museum's security guard.
Ruth works out a plan to rid herself of both Milton and Edward, and thus keep the museum. She tells Milton she wants him to break into the museum that night and steal some of the displays so that the museum can collect the insurance money to help it pay its debts. In return, Ruth promises Milton she will pay him $100,000 and supply him with a new identity so he can start a new life abroad.
However, Ruth knows that Edward will be working late cataloguing the museum's pieces on the night that Milton will break in. As Milton is in the middle of his burglary, Ruth shows up and shoots him. The noise brings Edward to investigate, and Ruth shoots him too, then arranges the scene to make it look like Edward discovered Milton in the middle of a burglary and that Edward and Milton shot each other at the same time.
When Columbo investigates, he discovers that there is a tragic past to the Lytton family that has a bearing on the case.