Dial M For Murder (1954)

In London, wealthy Margot Mary Wendice had a brief love affair with the American writer Mark Halliday while her husband and professional tennis player Tony Wendice was on a tennis tour. Tony quits playing to dedicate to his wife and finds a regular job. She decides to give him a second chance for their marriage. When Mark arrives from America to visit the couple, Margot tells him that she had destroyed all his letters but one that was stolen. Subsequently she was blackmailed, but she had never retrieved the stolen letter. Tony arrives home, claims that he needs to work and asks Margot to go with Mark to the theater. Meanwhile Tony calls Captain Lesgate (aka Charles Alexander Swann who studied with him at college) and blackmails him to murder his wife, so that he can inherit her fortune. But there is no perfect crime, and things do not work as planned.

Ex-tennis pro Tony Wendice decides to murder his wife for her money and because she had an affair the year before. He blackmails an old college associate to strangle her, but when things go wrong he sees a way to turn events to his advantage.

Tony Wendice learns that his wife, Margo had an affair but even though it's over, he decided to kill her but chose to bide his time. He waited until Mark Halliday, his wife's boyfriend, returned to town. He then placed his plan in order. He summoned a man, whose reputation is a bit shady, and reveals that he knows his secrets but also tells him about his wife and her boyfriend and that they are each the beneficiary of their estates. He gets the man to agree to kill his wife and he has laid out what appears to be perfect plan. Only thing is the man was the one who was killed. Wendice trying to cover everything up, decides then to make it appear that Margo had an ulterior motive for killing the man. And it appears to be working except Halliday doesn't believe she's guilty and the police uncover a few anomalies.