Tony Wendice, an English retired tennis player, is married to wealthy socialite Margot, who has had an affair with American crime fiction writer Mark Halliday. Unbeknownst to them, Tony knows about the affair, and is planning to have Margot killed so he can inherit her fortune.Dial M for Murder 1954. Tony invites an old acquaintance from the University of Cambridge, small-time criminal Charles Swann, to his London flat. He tells Swann about Margot’s affair, and that, six months earlier, he had stolen her handbag, which contained a love letter from Mark, and anonymously blackmailed her. Tony tells Swann that he has been following him for a year, and knows that he swindled and murdered his landlady. After tricking Swann into leaving his fingerprints on the letter, Tony offers to pay him £1,000 to kill Margot; if Swann refuses, Tony will turn him in to the police as Margot’s blackmailer. After Swann agrees, Tony explains his plan: the following evening, he will go with Mark to a party, leaving Margot at home while hiding her latchkey under the carpet. Swann is to sneak in and, after Tony telephones the flat from the party, strangle Margot when she answers the call. The following night, Swann enters the flat while Margot is in bed and waits. Tony calls the flat, and when Margot comes to the phone, Swann tries to strangle her, but she stabs Swann in the back with scissors, killing him. When Margot grabs the phone and pleads for help, Tony tells her not to call the police. After sending Margot to bed, Tony moves what he thinks is her latchkey from Swann’s pocket into her handbag, and plants Mark’s letter and Margot’s stocking on Swann to make it look like she killed him in cold blood.