To Catch a Thief is a 1955 American romantic thriller film directed by Alfred Hitchcock, from a screenplay by John Michael Hayes based on the 1952 novel of the same name by David Dodge. The film stars Cary Grant as a retired cat burglar who has to save his reformed reputation by catching an impostor preying on the wealthy tourists of the French Riviera. Grace Kelly stars opposite him as his romantic interest in her final film with Hitchcock.
Retired jewel thief John "The Cat" Robie is suspected by the police in a string of burglaries on the French Riviera. When they come to his hilltop villa to question him, he slips their grasp and heads to a restaurant owned by his friend Bertani. When the police arrive at the restaurant looking for Robie, Danielle Foussard, the teenage daughter of a staff working in the restaurant Foussard, who has a crush on him, spirits him to safety.
Robie realizes he can prove his innocence by catching the new Cat in the act. He enlists the aid of an insurance man, H. H. Hughson, who reluctantly discloses a list of the most expensive jewelry owners currently on the Riviera. American tourists Jessie Stevens, a wealthy nouveau riche widow, and her daughter Frances, top the list. Robie strikes up a friendship with them. Frances feigns modesty at first, but kisses Robie at the end of the night before retiring to her room.
The day after, Frances invites Robie to a swim at the beach, where Robie runs into Danielle, who is jealous about his interest in Frances.
When Frances accompanies Robie on a "picnic" to a villa, she reveals that she knows Robie's real identity. He initially denies it, but concedes it that evening when she has invited him to her room to watch a fireworks display. There they kiss passionately.
The next morning, Frances's mother Jessie discovers her jewels are gone. Frances accuses Robie of using her as a distraction so he could steal her mother's jewelry. The police are called, but by the time they reach Jessie's room, Robie has disappeared.
Later, Robie is staking out an estate at night when he is attacked by an unknown assailant. A second attacker raises a wrench and appears to hit Robie, who falls off the estate's seawall into the water. But when the police reach the body in the water, it turns out to be Foussard, one of the staff at Bertani's restaurant.
The police chief publicly announces that Foussard was the jewel thief, but, as Robie points out privately in the abashed Hughson's presence, this would have been impossible because Foussard had a wooden leg, and could not climb on rooftops.
Foussard's funeral is interrupted by Danielle's loud accusation that Robie is responsible for her father's death. Outside the graveyard, Frances apologizes to Robie and confesses her love. Robie asks Frances to arrange his attendance at a fancy masquerade ball, where he believes the Cat will strike again.
Robie accompanies Frances to the ball dressed as a masked Moor. The police hover nearby. Upstairs, the cat burglar silently cleans out several jewel boxes. When Jessie addresses the Moor as "John" and asks him to go and get her "heart pills", the authorities are tipped off as to his identity. Upon the masked Moor's return, the police wait as he and Frances dance together all night. When the masked Moor and Frances go to her room, the mask is removed: it was Hughson, who switched places with Robie to conceal Robie's exit.
Robie lurks on the rooftop, and his patience is finally rewarded when he spots a figure in black. However, just as his pursuit begins, the police throw a spotlight on him and demand he halt. He flees as they shoot at him, but he nonetheless manages to corner his foe with jewels in hand. Unmasked, his nemesis turns out to be Danielle. She loses her footing on the roof, but Robie grabs her hand before she can fall. While she hangs in his grasp, he forces her to confess to the police and admit that Bertani was the ringleader of this gang.
Robie speeds back to his villa. Frances follows to convince him that she has a place in his life. He agrees but looks less than thrilled when she says, "Mother will love it up here."