Dial M for Murder

Dial M for Murder is a 1954 American Detective fiction film directed by Alfred Hitchcock, starring Ray Milland, Grace Kelly, Robert Cummings and John Williams. The screenplay and the successful stage play on which it was based were written by English playwright Frederick Knott. The play premiered in 1952 on BBC television, before being performed on stage in the same year in Londons West End in June, and then New Yorks Broadway in October. The movie version was released by Warner Bros.

Mark visits and Margot introduces him to Tony as an acquaintance. Tony sends the two lovers out for the evening and meets at the flat with an acquaintance from Cambridge University, C. A. Swann Anthony Dawson, who has become a criminal. Tony has secretly been following Swann so he can blackmail him into murdering Margot. Tony tells Swann about Margots affair, including a love letter from Mark which she once kept in her handbag. Six months prior, Tony stole the handbag and anonymously blackmailed her. After tricking Swann into leaving his fingerprints on the letter, Tony offers to pay him 1,000 24,500 today to kill Margot if Swann refuses, Tony will turn him in to the police as Margots blackmailer.When Swann agrees, Tony explains he will take Mark to a party, leaving Margot at home and hiding her latchkey outside the front door of the flat. Swann must sneak in when Margot is asleep and hide behind the curtains in front of the French doors to the garden. Atpm Tony will telephone and Margot will go to the phone. Swann must kill her, open the French doors, leave signs suggesting a burglary gone wrong, and exit through the front door, hiding the key again. ........

Source: Wikipedia