Dial M for Murder (1954), a crime thriller film directed by Alfred Hitchcock, is centred on a husband, a retired professional tennis player, who discovers that his wealthy wife had an affair and believing that she would leave him, the husband blackmails an old classmate into agreeing to murder her. However, when the plan goes awry and the wife kills her would-be killer, the husband devises a method of framing her for the murder. Based on a stage play of the same name by Frederick Knott that ran successfully in London and New York, the film was also a box office hit when it opened in 1952 on London’s West End and New York’s Broadway, earning an estimated $2.7 million only in North American box office sales in 1954. The film was the first of the three Hitchcock movies that were graced by the appearance of Grace Kelly, who later also appeared in his Rear Window and To Catch a Thief (1955).

The story of Dial M for Murder is set in London, where Tony Wendice, a retired English professional tennis player, who does not earn very much in his current line selling sports, but is apparently living happily with his young and wealthy socialite wife Margot. However, the problem started with the arrival of Mark Halliday, a well-known murder mystery writer from America, with whom Margot had a passionate love affair a year earlier.

When Mark arrives from America to visit the couple, Margot tells him that she had decided to break off their relationship forever and had destroyed all his letters, except one, as she does not want her husband to know about the matter. But things have now become complicated, as that single love letter which was preserved, was somehow stolen from her handbag and she has received blackmail threats about the letter from the unknown thief.

Although Margot wanted to hide about her secret from her husband, Tony was very much aware of it, as he was the thief of the letter and the stunning revelation of the fact about his wife made him scared, as he thought, Margot would leave him for Mark, which would make him penniless. He, therefore, hatches a plan to kill Margot and inherit her wealth, before it is too late and desperately contacts Charles Swann, an old friend from Oxford with a shady background, a list of creditors and petty crimes, a previous spell in jail and a court martial from the army. He told him frankly all about Margot's affair with Mark and also confided that six months earlier, he stole a love letter written by Mark from Margot's handbag and anonymously blackmailed her.

In between their conversation, Tony cleverly entrapped Swann by leaving his fingerprints on the letter and after offering £1,000 to murder his wife the very next night, when he and Mark will be away attending a stag party, threatening to turn him in as Margot's blackmailer, unless he agrees to his proposal to kill Margot.

Tony’s diabolical plan clearly reveals his conscienceless, greedy character. In fact, taking revenge for the infidelity on the part of his wife was not the motivation for his plan to kill Margot. His prime concern was to inherit her wealth in her absence to support his newly accustomed luxuriant lifestyle, which as a retired tennis professional, he cannot afford. His plan for Swann to strike while he will be away at a stag party, along with Mark and Margot is certain to be in bed. Swann is to enter the front door, which is always unlocked and will enter their flat with Margot's latchkey, which Tony will steal from her and hide under the staircase rug, just outside the flat door. After that, Tony will call his wife at a prearranged time, which will bring her to the telephone and Swann will make the use of the opportunity to carry out the murder.

As their home is located in Maida Vale in West London, Tony has to dial M for Maida Vale, giving the film its title. Nevertheless, Tony also instructed Swann to whistle over the phone, confirming him about the completion of the job, create a scene of burglary in the flat to misguide the police and keep the latchkey back in its place under the staircase rug as it was, before leaving the building.

However, despite of everything, the plan went wrong, when Margot fatally stabbed Swann with scissors, while he was trying to strangle her with his scarf. On hearing Margot's pleading for help instead of Swann's whistle, Tony sensed a problem and immediately rushed home. He then tries to pacify Margot, advises her not to speak about the incident to anybody and sent her to bed. After that, he called the police and recovering a key from Swann's pocket coolly kept it in Margot's handbag. However, unknown to Tony, Swann had actually taken the key from the hiding place and then replaced it. Therefore, the key that Tony took out of Swann’s pocket was actually the dead man’s own latchkey. Nevertheless, finding his original plan dashed, he immediately hatched a new plan to kill Margot and proceeded to make it appear that Margot murdered Swann when he came to the apartment, as he had been blackmailing her over the stolen love letter. In fact, as he expected, Margot was arrested, convicted for the murder and was sentenced to death.

On the day before Margot's scheduled execution, Mark visits Tony and informs him that he has devised a story to save Margot and following his story, he approaches Tony to confess to the police that he had himself planned to murder his wife and had sent Swann to carry out the job. If he agrees, it would be rather injurious to his reputation and he would go to the jail for a while, but Margot would be saved. As Mark persists Tony to agree and Tony resists saying that the idea is ridiculous, Inspector Hubbard arrives on the scene unexpectedly and Mark hides in the bedroom. While Inspector Hubbard asks Tony about the large sums of cash he had been spending recently around town, he tricks Tony into revealing that his latchkey is in his raincoat pocket. He then inquires about Tony's attaché case and Tony claims to have misplaced the case, while Mark finds the briefcase on the bed, full of banknotes. The unexpected discovery leads Mark to deduce that the money in the briefcase is Tony's intended payoff to Swann and coming out from his hideout, he confronts Tony and also explains his theory to Hubbard. But Tony in his turn twisted the fact by saying that the cash was really meant for Margot's blackmail payment to Swann, which he had concealed to protect her. As Inspector Hubbard apparently appeared to accept Tony’s explanation, Mark left the place angrily, while Hubbard discreetly swaps his own raincoat with Tony's.

After a while, followed by Mark, Hubbard re-entered the flat, in the absence of Tony, using Tony’s key. By that time, he had already discovered that the key in Margot's handbag was actually Swann's own latchkey and deduced that Swann had put the Wendices' key back in its hiding place after unlocking the door. Now, after re-entering the flat using Tony’s key, he became confident that he correctly suspected Tony of having conspired with Swann and developed an elaborate ruse to trap him. According to his plan, when Margot was brought to the flat by the plain dress police officers, she unsuccessfully tried to unlock the door with the key in her handbag and then entered through the garden, which proved that she was unaware of the hidden key and is therefore innocent. Earlier, Margot's handbag was returned to the police station, which Tony retrieved after discovering that he had no key. However, as the key from Margot's bag did not work, he used the hidden key to open the door, demonstrating his guilt and exonerating Margot. Finding all his escape routes blocked by Hubbard and another policeman, Tony knew that he has no other way, but to face the consequences. But he keeps his cool, calmly makes himself a drink and congratulates Hubbard.

However, despite the film’s popularity, Hitchcock did not consider Dial M for Murder as one of his major works, perhaps because he was bored by a story that, except the attempted murder, relies little on surprise or suspense to entertain the audience or perhaps because it was connected with the production constraints that were imposed on filmmakers at the time in efforts to distinguish movies from the possible threatening encroachment of television. Interestingly, although shot in cinemascope and in dual-strip polarized 3-D, the film was shown to the public in most of the theatres in the ordinary 2-D, a standard flat format, but later re-released in 3-D in the 1980s. Nevertheless, Dial M for Murder, a drawing-room perfect murder movie with a theatrical story, supported by an excellent screenplay, breathtaking cinematography and top-notch performances by Ray Milland in the role of the Machiavellian and cynical Tony Wendice, Robert Cummings as Mark Halliday and Grace Kelly playing the role of Margot, is one of the best thrillers of cinema history.