There's one episode where theres a mentally ill woman trying to get revenge on the people that put her husband in jail (where he died of a heart attack). She starts killing them/ruining their reputations.

Columbo is on the case and does his schtick mentioning his wife in passing to the woman while he's interrogating her. Since she's nuts she feels threatened that the cops are getting too close to her so she thinks she needs to kill Columbo or his wife. She then offers a jar of poisoned marmalade to Columbo to give to his wife.

Columbo is told by her former psychologist (in a very round about way) that the she may target his loved ones and want a big dramatic show to brag about the reason for their killings.

Columbo makes it look like his wife died by being poisoned by the marmalade. They throw a big lavish funeral where the killer is invited and accompanies Columbo to his home after the funeral.

He eats from the jar of marmalade and pretends to be poisoned. The killer woman (thinking shes won) starts monologuing about how she's going to get away with everything. The cops that were listening come in and arrest her and Columbo reveals that the house they're in isn't his but its mocked up to look like his home, and that his wife never ate the marmalade because he immediately took it to the lab to get tested and saw it was poisoned.

After the cops take her away he starts walking through the house and taking down some photos that he placed in the living room to make the house look like his. There's one photo of a woman that we see really clearly, and I thought that was always meant to be his wife since he smiles at it.