In 1958 New York City, Tom Ripley is approached by shipbuilding magnate Herbert Greenleaf, who believes that Ripley attended Princeton with his son Dickie. Greenleaf pays Ripley one thousand dollars to travel to Italy, where Dickie has settled, and persuade him to return to the United States. On a first-class ocean liner voyage, Ripley pretends to be Dickie and befriends American socialite Meredith Logue.
In the seaside village of Mongibello, Ripley befriends Dickie and his American girlfriend Marge Sherwood by claiming to be a former Princeton classmate. He enjoys Dickie's extravagant lifestyle and becomes obsessed with Dickie himself, but Dickie's wealthy friend Freddie Miles mistrusts Ripley and treats him with contempt. When he returns from Rome, Dickie is disturbed to find Ripley dressed in his clothes and dancing in front of a mirror. Dickie impregnates a local young woman called Silvana and then spurns her, causing her to drown herself. Ripley, aware of what has happened, promises a guilt-ridden Dickie to keep the death a secret. After Dickie's father cuts off Ripley's travel funds, Dickie cancels a trip to Venice and tells Ripley that they should part ways, but Ripley convinces Dickie to take a final trip with him to San Remo.
Aboard a small boat, Dickie says that he has grown tired of Ripley and is going to marry Marge, while Ripley insists that Dickie is afraid of their feelings for each other. The argument becomes physical, and Ripley kills Dickie with an oar. Ripley takes Dickie's belongings and scuttles the boat. Realizing that locals frequently mistake him for Dickie, Ripley assumes Dickie's identity. He forges a letter to Marge, convincing her that Dickie has left her and moved to Rome. Ripley creates the illusion that Dickie is still alive by checking into one hotel as Dickie and another as himself, then fabricating an exchange of communications between the two. Through forgery, he is able to draw on Dickie's allowance, which allows him to live lavishly.
In Rome, Ripley runs into Meredith, who still knows him as Dickie, and accepts an invitation to attend an opera with her family. His ruse is threatened at the opera when he unexpectedly runs into Marge and her friend Peter Smith-Kingsley. Ripley rushes Meredith out of the opera house and rejects her advances. Later, Freddie shows up to Ripley's apartment looking for Dickie. When the landlady addresses Ripley as Dickie, Freddie realizes the fraud, so Ripley bludgeons him to death and disposes of his body. When the body is found, police visit the apartment to question "Dickie." Ripley forges a suicide note for Dickie that claims responsibility for Freddie's death. Under his real name, Ripley travels to Venice, where he again encounters Peter.
Dickie's father arrives in Italy, accompanied by private detective Alvin MacCarron. Ripley almost kills Marge after she discovers he has Dickie's rings, but they are interrupted by Peter. Mr. Greenleaf dismisses Marge's suspicions, and MacCarron tells Ripley that the police are convinced that Dickie, who had a history of violence, murdered Freddie before killing himself. MacCarron tells Ripley that Greenleaf intends to bequeath a large portion of Dickie's trust fund to him, to reward his loyalty to Dickie and ensure his silence.
Free and clear of his crimes, and with the income to finally live Dickie's lifestyle as himself, Ripley boards a liner to Greece with Peter. It is implied that they are now lovers. On board, Ripley is surprised to encounter Meredith. Ripley kisses her and promises to talk later. In his cabin, Peter tells Ripley he saw him kiss Meredith and demands answers. After apologizing for lying to him, a sobbing Ripley strangles Peter to death and returns to his cabin, alone.
