Tom Ripley is a young man struggling to make a living in 1950s New York City with his "talents": telling lies, forging signatures and impersonating people. While working at a party, he is approached by the wealthy shipbuilder Herbert Greenleaf, who mistakenly believes that Ripley attended Princeton with his son, Dickie. Greenleaf recruits Ripley, for $1,000, to travel to Italy to persuade Dickie to return home. During the trip to Italy, Ripley strikes up a friendship with an American socialite, Meredith Logue, while pretending to be Dickie.
In the Italian seaside town of Mongibello, Ripley charms himself into the lives of Dickie and his fiancée, Marge, partly through pretending to be a fellow jazz lover and alumnus of Princeton. Ripley becomes infatuated with Dickie's extravagant lifestyle; he also becomes obsessed with Dickie himself. Eventually, however, Dickie tires of him and starts spending more time with his Princeton friend Freddie Miles, a womanizer who treats Ripley with contempt. When Dickie impregnates a local woman, he rejects her and she drowns herself. Only Ripley knows what happened, and he promises to keep it a secret. One night, Dickie catches Ripley dressed in his clothes and pretending to be him in front of a mirror, which further alienates him from Ripley. When Dickie's father determines that Ripley has failed in his mission to bring Dickie home and cuts off his travel funds, Dickie cancels a planned trip to Venice and tells Ripley they should part ways, but offers to take him on a short, final trip to San Remo. They take a boat out, but when Ripley suggests they move in together, Dickie becomes angry and accuses Ripley of mooching. The two fight, and Ripley beats Dickie to death with an oar. Ripley scuttles the boat in a nearby cove.
Realizing that people easily mistake him for Dickie, Ripley decides to cover up the murder by impersonating him. He forges a letter to Marge, convincing her that Dickie has left her to live in Rome. He creates the illusion that Dickie is still alive by checking into one Roman hotel as Dickie and another as himself, creating an exchange of communications between the two. Through forgery, he is able to draw on Dickie's allowance, which allows him to live lavishly. He runs into Meredith, who has never met the real Dickie and believes that Ripley is actually Dickie; Ripley pretends to romance her to gain access to her wealthy circle of friends. His ruse is threatened when Marge arrives in Rome, so he breaks it off with Meredith to prevent himself from being exposed. Freddie shows up at Ripley's apartment looking for Dickie and is immediately suspicious. When the landlady addresses Tom with "Ciao Dickie", Freddie realizes the fraud, but Ripley beats him to death with a stone bust before he can tell anyone. After disposing of the body, Ripley is forced into a cat-and-mouse existence between the Italian police and Marge. Realizing that the police suspect Dickie of murdering Freddie, Ripley forges a suicide note to dispose of the Dickie persona once and for all. He then travels to Venice, where he meets Marge's friend, Peter Smith-Kingsley, and they develop feelings for each other.
Herbert Greenleaf travels to Italy to meet with the police, bringing along a private detective, Alvin MacCarron. Ripley prepares to kill Marge when she discovers Dickie's rings in his possession, but Peter interrupts them. Mr. Greenleaf dismisses Marge's suspicions, and MacCarron reveals to Ripley that the police are convinced that Dickie, who had a history of violence, murdered Freddie before killing himself. MacCarron further indicates that out of appreciation for Ripley's loyalty to Dickie—and to assure Ripley's silence—Mr. Greenleaf intends to bequeath Dickie's trust fund to Ripley. Free and clear of his crimes, Ripley boards a ship to Greece with Peter; it is implied that they are now lovers. Ripley is surprised to encounter Meredith, who knows him as Dickie and also knows Peter socially. Killing Meredith to avoid being exposed as an impostor is impossible because she is traveling with family. Ripley returns to his cabin and asks Peter to tell him about Ripley's good qualities. Sobbing, he strangles Peter.
