Strangers On A Train is a 1951 thriller by Alfred Hitchcock starring Farley Granger and Robert Walker. The story follows a tennis pro who on a chance meeting on the train, becomes unknowingly caught up in a murder pact with a charming psychopath. The film received an Academy Award nomination for Black and White Cinematography, as well as a spot on the AFI's list for "100 Years... 100 Thrills."
The lesson here is not to talk to strangers. Or maybe it's not to travel by train... Regardless, there is definitely a lesson, and once Robert Walker's character Bruno begins talking, you'll want to learn the lesson as quickly as you can in order to get away from him.
Tennis pro Guy Haines (Farley Granger) is traveling home by train when he accidentally bumps into Bruno (Robert Walker). Bruno recognizes Guy and strikes up a conversation, which increasingly turns more and more strange. At some point Bruno navigates the discussion to his ideas on staging the perfect murder and casually suggesting that they could swap victims. He reveals an eerie intimacy of details regarding Guy's marital difficulties and desire to be rid of his cheating wife. Bruno proposes the idea of murdering Guy's wife in exchange for Guy taking care of his father for him. He believes the genius of his "criss-cross" theory is that by performing a stranger's murder for them, and the other doing likewise, neither could be linked to the crime. Zero motive. Guy assumes this is simply a troubled individual he will never have to actually deal with again, and both hurriedly and cordially excuses himself from the conversation and train.
But Bruno believes that they reached some kind of formal arrangement in their talk, and proceeds with murdering Guy's wife. He then begins following Guy around and reminding him of their gentlemen's agreement. Not only is Guy now a suspect in his wife's murder, but he can't go to the police with info on Bruno because he has no evidence (and Bruno is right, there is no motive to peg him to the crime). But Bruno does have something he could use against Guy if he decides not to cooperate with the exchange. And if things don't go his way, he has already proved himself crazy enough to go through with it.
Strangers On A Train is so successful because it creates a thoroughly creepy character that is regrettably believable. Bruno is a pure psychopath with just enough charisma and charm about him to blend into the crowd. His good looks and gregarious personality allow him to strike up a conversation at will, and it's only through the course of the conversation that you realize how distorted is his thinking. Is he joking? Does he just have a warped "what if" mode of conversing about murder? No, he is literally deadly serious. And it's this singular performance by Walker that continues to captivate long after the specifics of the story have ended.