**SPOILERS** Since the disappearance at sea of her favorite niece Phyllis murder mystery writer Abigail Mitchell, Ruth Gordon, has strong suspicions that it was Phyllis' husband Edmund Galvin, Charles Frank, who was responsible for her death. In fact Abigail is convinced that he murdered her and made it look like a tragic accident.<br /><br />Knowing that there's no evidence to have Edmund arrested for Phyillis' death and deciding to take the law into her own hands Abigail cooks up this elaborate plan to do him in and make it look, like Phyllis' death, a tragic accident. Getting Edmund to secretly come over to her mansion to give him the combination to her walk-in safe, as she's about to leave on vacation for New York City, Abigail tricks him into going inside locking the startled and surprised Edmund in. With the safe being soundproof nobody at the mansion the butler maid and Abigail's personal secretary Veronica, Mariette Hartley, hear him screaming for help and the next day Edmund is found suffocated to death. Veronica discovered Edmund's body as she was about to put away, for safe keeping, Abigail's latest murder mystery manuscript.<br /><br />Lt. Columbo, Peter Falk, is called on the case involving the strange death of Edmund Garvin to determine if it's a murder or a tragic accident. Going through Edmund's apartment Columbo is puzzled to find out that he doesn't have a single photo of his late wife, who's been missing for just a month! This ties into what Abigail always felt about him in Edmund not being in love with Phyllis and also a suspect in her, in Abigail's mind, murder. <br /><br />Columbo a big fan, together with his wife, of Abigail's murder mystery novels has a hard time realizing that she in fact was responsible for Edmund's death. All the evidence points to Abigil including a pair of missing car keys that was Edmunds. This all proved that Abgail was in fact in the house, not on her way to the airport, when Edmund was locked inside the walk-in safe.<br /><br />Going through all the evidence Columbo comes up with this strange conclusion that Edmund must have left some evidence inside the safe in writing to who his killer is. That conclusion is quickly checkmated when it's found out that Edmund didn't even have a pen or pencil as well as light, with the safe light-bulb burned out, on him to write it. There's also something very odd that's inside the safe that has been on Lt. Columbo's mind ever since he came on the case. This has to do with the black paint residue that was found under the dead Edmund's fingernails and on his belt buckle! <br /><br />It's that evidence, when put together with a number of other items in the safe, that in the end hangs Edmund's murder on the tricky and very cunning mystery writer Abigail Mitchell. Edmund let Abigail unknowingly convict herself in his final attempt as the air in the safe was being used up, by his breathing, in using burnt out matchsticks to write on Abigail last manuscript who murdered him: Abigail Mitchell!