Strangers on a Train (1951), a psychological thriller,  directed by Alfred Hitchcock, reflects the persisting apprehension in his life that he would be accused of a crime in which he was not involved. The story of the film revolved around two strangers who first time met on a train, one of whom is a psychopath, who suggested to the other, a tennis player, that they exchange murders so that neither would be caught for the absence of motives. In addition, both would have strong alibis for the time of the crime and there would be no connection between the killer and the victim. But eventually, the tennis player became the obvious suspect in the strangulation of his wife, although he was not even aware of it.

The plot of the film, based on the first novel by Patricia Highsmith of the same name, is all about that unusual criss-cross murder deal that would have worked perfectly, except for the detail that only one of the strangers agreed to it.

The story of the film Strangers on a Train starts with the first meeting of Guy Haines, a professional tennis player, with conservative, plain black dress shoes and Bruno Antony, a rich playboy, with a lobster-claw patterned necktie, and a tie pin with his inscribed name, as they sat in the lounge car of a train, travelling from Washington DC to New York. Bruno, a self-proclaimed tennis fan, immediately recognised Guy Haines, moved to sit next to him and initiated a conversation, showing his detailed knowledge about Guy’s private life, including his target to divorce his unchaste wife Miriam and marry Anne Morton, the daughter of a US Senator. In the course of the conversation, when Bruno was searching for his matchbox to light up a cigarette, Guy offered him his lighter, embossed with the inscription A to G and an image of two crossed tennis rackets in the corner.

While appreciating the beauty of the light, Bruno said that is sure that the letters A and G stand for Anne and Guy and he even knew that Guy was anxious to rid himself of his wife to marry Anne without any further delay. However, as Guy was offended by his remark, Bruno quickly apologised for being too friendly.

Later, over lunch in his private compartment, Bruno reveals that his father is hateful, tyrannical and spiteful and he wants him to die. At that point, he also suggests his morbid idea of a perfect murder in which he would murder Guy's wife, Miriam and in return, Guy would murder Bruno's father, enabling him to acquire an inheritance and neither would ever be suspected due to no apparent motive. Although Guy pretended to be amused by the idea, he was eager to hurriedly get away from Bruno in disgust and forgot to take back his engraved lighter from Bruno, which he did not return to him.

When the two men parted, Guy was sure that he would never hear from Bruno Antony again, but Bruno believed that they already had an agreement and while he was determined to proceed on his mission to kill Haines’s wife, he also expected Guy Haines to uphold his end of the bargain and kill his father.

After leaving his bags with one of his friends, Guy walked over to Miller's Music Store where his estranged wife Miriam was an employee. Although Miriam had confessed to being pregnant by another man and they had a meeting scheduled with a divorce lawyer, the bespectacled promiscuous female with thick lenses coolly informed Guy that she was no longer interested to end their marriage. She also threatened him to claim that he is the father to thwart any divorce attempt. During their hot argument, Guy grabbed Miriam and angrily shook her, while their loud argument was witnessed by many other customers, before they were restrained by the authority.

That evening, Bruno took the train to Metcalf, located Miriam's address from the phonebook of a phone booth and then kept an intense watch on Miriam's plain, small-town house from a bus stop across the street. After some time, the bespectacled Miriam burst out of the front door, along with her two male friends and rushed to catch a Metcalf Transit Lines bus. Bruno followed to reach a local carnival park and lit a cigarette with Guy's lighter at the entrance. However, Miriam first noticed Bruno watching them, while they were enjoying the ice cream cones. As she dragged her friends along with her, she looked back to make sure she was being followed by her new admirer. Their next stop was the merry-go-round, where Bruno sat on one of the bobbing, prancing horses behind Miriam. At the Tunnel-of-Love boat ride, he followed them by another boat to dock at a nearby Magic Isle, when suddenly, Miriam purposely evaded her friends to run into Bruno and her face was illuminated by the flicking flame of Guy's lighter as Bruno wanted to confirm whether she was Miriam. Immediately after that, Bruno's gloved hands grabbed her by the neck, while her glasses tumbled onto the grass and fell next to Guy's lighter. However, before quickly returning to his boat and shoved off, Bruno retrieved both Miriam's broken eyeglasses and the lighter from the grass. But while Bruno was walking through the crowd to escape, he was distinctly noticed by the Boat Man vendor operator for his suspicious attitude.

During the time of the murder, Guy was on a train heading southward from New York City to Washington DC and was identified by a drunken Delaware Tech University Professor Collins, unknowingly establishing an alibi for his whereabouts at the time of Miriam's murder. However, when he arrived at his DC apartment by taxi, he was interrupted at his front door by Bruno, who informed him about the murder of Miriam and produced her eyeglasses with a cracked right lens as the proof. The stunned Guy responded in horror by calling him a maniac, but Bruno reminded him of their bargain and said that as he had completed his part by murdering Miriam, Guy must now honour their deal, by killing his father. Guy threatened to call the police, while Bruno coolly explained that in that case both of them would be arrested for the murder as it was planned by them together and only Guy had a real motive to eliminate his wife. After that, Guy visited Anne Morton’s house, where he was informed by her father about the murder of his wife and Anne's sister, spectacled Barbara opined that the police would primarily suspect Guy as the murderer since he had a motive. The police questioned Guy, but his alibi fell through, as the drunk professor on the train failed to identify him and could not remember their encounter. However, instead of arresting Guy, the police assigned an around-the-clock escort to watch him.

Back in Washington DC, Bruno introduced himself to Anne to create pressure on Guy, appeared at a party at the Senator’s house and to amuse another guest, playfully started to demonstrate how to strangle someone, by putting his hands around her neck. At that moment, he suddenly spotted Barbara observing him with horror from behind her spectacles, with her glasses and physical appearance strongly resembling Miriam. The resemblance created havoc in Bruno, as it triggered a flashback and he uncontrollably began to choke the woman. While other guests intervened to stop him from strangling the woman, Bruno fainted on the floor. Later, when Barbara told Anne that Bruno was looking at her strangely while strangling the other woman, Anne realised that Barbara's resemblance to Miriam made Bruno shaky and the realisation made her suspicious about Guy. When she confronted Guy about it, he told her all about the crazy deal.

Meanwhile, Bruno sent Guy a package containing a pistol, a house key and a map showing the location of his father's bedroom for obvious reasons. But when Guy stealthily crept into Bruno's father's room to warn him of his son's murderous intentions, he found to his surprise, Bruno in place of his father, as he had anticipated Guy's duplicity and pretence. As it became evident to Bruno that Guy would not reciprocate and fulfil his end of the bargain, he tried to mislead Anne by saying that Guy asked him to search his missing lighter at the site of the local carnival park, where Miriam was murdered. However, Guy correctly deduced from it that Bruno has planned to frame Guy by planting his lighter at the amusement park later that night, as evidence to incriminate him for the murder of his wife.

However, Guy Haines was determined to stop Bruno before he could complete his mission, but at the same time, he did not want to skip his tennis tournament match at the US Open at Forest Hills Stadium. He was confident that he could reach Metcalf in time to prevent Bruno from planting his lighter after dark on the Magic Isle of the amusement park, if he could win in three quick sets and evade police after the match with the help of Anne and Barbara. However, deep in his mind he also knew that if he could not snatch a quick win in three straight sets, he might not be able to reach Metcalf in time. As luck would have it, Guy had to earn a win after a long gruelling match and after that, he successfully evaded the police officers to rush at the entrance to an awaiting taxi, pre-arranged by Anne and Barbara, that took him to Penn Station to board a train to Metcalf.

By the time Guy entered the park, Bruno was recognised by a carnival worker from the night of the murder and pointed out him to the police, but they mistakenly thought he was pointing at Guy. In the meantime, as Guy called Bruno, Bruno jumped onto the merry-go-round to evade him and Guy also followed him desperately. To add more confusion to the scene, a police officer fired at Bruno, believing him to be Guy trying to escape them, which killed the operator of the merry-go-round, causing the ride to spin violently out of control. However, while all the terrified riders were screaming hysterically at the dizzying speed of the ride, Guy and Bruno were engaged in fighting aboard the wildly-speeding ride for the possession of the lighter. Finally, a veteran carnival worker came forward to take the risk of crawling underneath the structure and applied the brakes to stop the crazily spinning ride abruptly, causing the carousel to spin off its support. As a result, the entire structure broke apart and exploded into pieces before coming to a dead halt, trapping Guy and the mortally injured Bruno underneath, while the other riders were tossed off. While the worker, who had called the police, identified Bruno as the man whom he saw the night of the murder, Bruno died and the fingers of his left hand opened to reveal the engraved lighter of Guy, which proved that he was the murderer, not Guy.

Strangers on a Train, directed by Alfred Hitchcock and released on 30 June 1951, is not a psychological study, but a fabulous thriller, since Guy clearly had a motive to murder his wife and on the day of her death, he was seen in a public fight with her. Usually ranked among the best of Hitchcock, its appeal is probably the linking of a unique plot with weird creepiness. Although the film received mixed reviews upon its release, it was selected by the Library of Congress in 2021, for preservation in the United States National Film Registry, as culturally, historically, or aesthetically significant.