The episode begins with Ken Franklin paying a visit to Jim Ferris, a writer with whom Franklin created a character named Mrs. Melville. He points a gun at Jim, but Jim is not intimidated because he sees that Franklin's finger is not on the trigger and that the cylinder is empty. Franklin then comes in and apologizes for his behavior on a previous day when he got angry at Ferris. He opens a bottle of wine and offers a toast to what he calls their "divorce". The audience learns that Ferris and Franklin have co-authored 15 books together, starring the aforementioned Mrs. Melville, but now Ferris has decided to work on his own as a writer. As they are talking, Franklin discreetly slides a cigarette lighter onto a table. He then talks Ferris into going with him to his cabin and doing some fishing.
In the parking lot, Franklin says he made a list of things he wanted from the office, but when he hands it to Ferris, it is a list of names. Ferris hands it back. As they are about to get in the car, Franklin says he has to run back up to the office to get his lighter because he forgot it there. When he gets upstairs, he trashes the office, then leaves the list of names in a drawer. He grabs his lighter on the way out.
Franklin and Ferris head for the cabin. Along the way, Franklin stops at a store where a woman named Lilly La Sanka works. He gives her one of their books because she is a big fan. She asks who is with him this week, but he says he's alone. Then he goes to a pay phone where he calls Ferris's wife Joanna. He tells her that he left Ferris at the office and is now at his cabin.
They arrive at Franklin's cabin, where Ferris calls his wife and tells her he's working late and won't be home for dinner. While Ferris is on the phone, Franklin shoots him. A few minutes later, Joanna calls Franklin and tells him that she heard a gunshot while talking to Ferris on the phone. He tells her not to worry, and that he's leaving right away.
At the office, the police are there, but they are not convinced of Joanna's story about the gunshot. She continues to tell them over and over what she heard, but they are skeptical because his body is not there. She gets upset and goes to get a drink of water. Columbo is in the hallway, and he convinces her to let him drive her home. When they get there, he makes her an omelet. While he's cooking, she tells him that Ferris is the real writer and that Franklin got to share the glory but did none of the work. She also tells him that Ferris decided to go out on his own and that sooner or later people will probably realize that Ferris was the only writer.
Franklin arrives at Joanna's house and immediately asks Columbo if Ferris has been found yet. Columbo counters by asking how Franklin knew Ferris was gone. Franklin says he heard about it on the radio. Then he tells Columbo that this is a professional killing. He takes Columbo to the office and digs out the list of names that he put there earlier. The names on the list are mobsters, and Franklin tells Columbo that Jim was going to write an expose on organized crime. Columbo is skeptical because he doesn't understand why a professional killer would get rid of the body. He also comments that the paper is folded like it was being carried in someone's pocket. He wonders aloud why Ferris would have folded it up before he put it in the drawer. Franklin says that Ferris used to fold up his papers and use it as a bookmark. He gives Columbo some of the Mrs. Melville books to read. As Columbo goes to leave, he turns and asks why Franklin didn't take a plane instead of driving back. Franklin said he wasn't thinking clearly so he just jumped in the car, and besides, he wouldn't have saved that much time.
When Franklin gets home, he puts Jim's body in his yard. Then, he calls Columbo and tells him he thinks he'd better come over right away. He tells Columbo that the body was there when he got home. Columbo asks why they would leave Jim's body on his lawn, and Franklin said it was a warning from the mob to keep him from completing the book. He tells Columbo he's going to have a really hard time finding the killer. Columbo starts to leave, and Franklin asks him to keep him posted. Columbo promises to do so, then asks Franklin to tell him again exactly what happened. Franklin tells him he found the body, rushed inside, and called Columbo. Columbo remarks that Franklin also opened his mail, and he says that if it was him who found his partner dead, he'd never think to open his mail. Franklin claims he did it to distract himself.
The next day, Columbo takes an insurance agent named Mr. Tucker out for a hot dog, then asks him if he can find out if his company wrote an insurance policy for Jim Ferris and Ken Franklin. When Tucker hesitates, Columbo offers to get a court order.
That evening, Franklin is at the theater with a young woman. As he is leaving, Lilly La Sanka calls to him. She asks him to come have a drink with her, but he declines. Then she tells him that she'll have to tell her story to someone else. She says that her story is a mystery, and it's all about a witness to a crime. Franklin gets rid of his date and takes Lilly out for dinner. He tries to flatter her, and she tells him that she's interested in him and that she saw Jim in his car. He agrees to pay her $15,000 to keep quiet.
Columbo goes to see Franklin and finds him in the middle of a photography session and interview. He tells the interviewer that he doesn't think he'll write anymore. After the interviewer leaves, Columbo returns Franklin's books and then tells him that everyone that they interviewed from the list of mobsters has denied ever hearing of Jim Ferris. Franklin tries to leave, but Columbo follows him out the door and says that he checked the phone records in San Diego. The records show a call from his cabin to the Ferris's house. Franklin explains that he called Joanna from the cabin and spoke to her for a few minutes. He then gets in the car and drives to Lilly La Sanka's store. He gives her the money and some champagne, then asks her to make dinner for the two of them that night. At dinner that night, he gets her drunk, then tries to get her to go out on the lake for a swim. She refuses, saying that she doesn't trust him out there. While she is looking at all the money, he wraps up an empty champagne bottle and kills her with it. Then he dumps her body and the two empty bottles in the lake. He flips her boat over, then swims to shore.
Columbo shows up at Franklin's cabin and asks him about Lilly. Franklin at first says he doesn't know her, but then admits he bought supplies at her store. Columbo says it's odd that she would go out on the lake all alone like that. Then Columbo asks about the night life around there, and Franklin says there really isn't one. Columbo says that's strange because he called the night before but no one answered.
Columbo goes to the grocery store to look around. He wanders into Lilly's home, which is in the back of the store, and he finds a champagne cork that had flown across the room the night before. He then sees a copy of a Mrs. Melville book on her shelf. When he opens it, he sees that it has been signed by Franklin.
Columbo goes to see Joanna Ferris and tells her that he thinks Franklin killed her husband and Lilly. She refuses to believe it. Columbo tells her Franklin needed money because he was spending like crazy. Franklin and Jim had each other insured, so Jim's death would bring Franklin a lot of money. Columbo says that Lilly must have known something and tried to blackmail Franklin. He says that he checked with the bank, and Franklin took out $15,000 the day before, then put it back in a day later. He asks her to tell him everything she knows about Ferris and Franklin. She starts talking.
Franklin goes to his office to move his things, but Columbo is waiting for him. Columbo tells him he's there to arrest him. Franklin remains calm and says that Columbo can't prove anything. Then Columbo tells him that the way he killed his partner was actually an idea for a book that Ferris came up with. He finds the scrap of paper where Jim wrote it down and reads it to Franklin. An officer comes to arrest him and Franklin turns and says that the irony is that was actually his idea. He must have told it to his partner 5 years ago, but he never thought that Ferris wrote it down.