Based on David Dodge’s novel and directed by Alfred Hitchcock, a former jewel thief is suspected of a string of robberies and tries to find the robber while the daughter of a wealthy woman romances him.
In France a woman shouts that someone stole her jewels. A thief dressed in black robs jewelry at night. Columnist Art Buchwald suggests that the cat burglar John Robie may be responsible for the series of robberies.
John Robie (Cary Grant) sees a car deliver five men in his driveway, and he loads a shotgun. Two men come in and ask him to accompany him on an investigation. He goes upstairs to change, and a shot is heard. They break into his room, and he escapes in his car. They get into their car and chase him. John gets out of his car and gets on a bus. He gets out at the harbor and goes into a restaurant. He tells Bertani (Charles Vanel) that he has not stolen jewelry in fifteen years. He wants his comrades to know he had nothing to do with the robberies. In the kitchen he tosses a bottle to a threatening cook. John says the thief is imitating him in every detail. John says he will catch the imitator himself by anticipating his next move. He needs information on who has jewelry that deserves to be stolen. Bertani tells him about someone who may be the cat burglar. Bertani arranges for John to be taken to Cannes, and John follows a man with a limp.
Danielle Froussard (Brigitte Auber) takes John in a speed boat. She knows he escaped when the Germans bombed the prison. He says they fought for six years to earn their paroles. He asks her to take him to the beach club at Cannes, and she points out a police plane. He hides in the boat. John changes to swim trunks and mingles with people at the beach. He gets a phone call from Bertani, who tells him the thief will find him.
John is dressed at a flower market and tosses a coin. H. H. Hughson (John Williams) tells him he insures the jewelry. He asks John if he has been married, and John says no. He tells John he is a bad risk. John says he is taking the risks, and Hughson will get the jewelry back. John asks for names and descriptions of the jewelry. Men grab John amid many flowers.
John and Hughson drink and have lunch on a terrace. John says he needs to find some evidence for the examining magistrate while he is on provisional liberty. John admits he killed 72 people while fighting for the resistance. John says he stole so that he could live elegantly. He says he stole only from the rich, but he kept everything and gave nothing away. John tells Hughson he steals on a small scale by not subtracting a free meal from his expense account. Hughson hands him the list with names, addresses, items, and their value. John says he will go after Mrs. Stevens first.
At a dinner table Hughson advises Mrs. Stevens (Jessie Royce Landis) to put her jewelry in the hotel safe. Her daughter Frances Stevens (Grace Kelly) goes with her to gamble. John sees them and goes to the roulette table also. John drops a chip down a woman’s dress and claims it had high value. She reimburses him. John sits at a table with Mrs. Stevens, Frances, and Hughson. Mrs. Stevens calls John “Mr. Burns” and asks him to call her Jessie. She asks him why he has not made a pass at her daughter. John offers to escort them to their suite. Mrs. Stevens goes in, and Frances kisses John before she closes her door. John goes outside on a balcony and looks around.
Hughson tells John that the burglar got away with $35,000 worth of jewels. Hughson asks Mrs. Stevens to put her jewelry in the hotel safe, but she refuses. Frances comes in and invites Mr. Burns to go for a swim. Hughson hints to John that they should be doing something together, but John puts him off.
John and Frances meet in the lobby, and John gets a written message. It warns him he has used up eight of his nine lives. At the beach Danielle waves to John and swims to a float. John follows her there. Danielle asks him about the American beauty. He asks who tipped off the police at the flower market. He says he got a message from the cat, who wants him out of town. Danielle wants him to go to South America with her. John tells Danielle that she is a girl, but Frances is a woman. Frances joins them, and John introduces them. John says they were talking about water skiing. Danielle says she looks older close up.
John gets dressed and notices water on his list, and he gives a man a tip. He sees Frances in a dress, and she asks if he has time for her now. He suggests cocktails at six. She says she has a car and a basket lunch to help him pick out a villa. He notices the man following him and accepts her offer. They get in her car, and the man follows them. While she is driving, she asks him to mention the kiss she gave him. She says after her father discovered oil, boys and their fathers were chasing her. He says he enjoyed the kiss and is awed by her efficiency. He asks her what she expects to get from him. He thinks she is there to buy a husband. She says the man she wants does not have a price. He says that eliminates him. They stop at a villa, and he says he likes a woman who knows her own mind. He suggests they look at the gardens without bothering the people. He notices that she does not wear jewelry. She says she does not like cold things on her skin. She asks about his wife, and he says he never married. She mentions the French girl, and he says she is jealous. He tells Frances she is an insecure, pampered woman accustomed to attracting men. He says she needs two weeks with a good man at Niagara Falls, but he is not inclined to give it to her.
They get in the car and are followed again. He says he is hungry and notices the car following them. He suggests they speed up, and she does so. They nearly hit a bus, and her tires screech on the curves. She slams on the brakes and stops for an old lady. He looks back and does not see the car. That car is stopped by an accident. He asks her to slow down. She says the police are following him, John Robie, the cat. She parks the car. He says he is Mr. Burns, not Robie. They open the basket and eat chicken. She asks him to call her “Francie.” She tells what she has noticed about him. She says he does not talk like an American. She asks if he is going to rob her mother first or someone else. She offers to help rob jewels. She knows the people that live at that villa, which is not for sale. He kisses her and asks if that is why she came up there. She asks for a date at eight, and he says he is going to the fireworks.
John gets a call from Bertani, who suggests he bring the rich American to his restaurant. Later John and Frances talk in her room and drink brandy. She asks if he is nervous about being in a room with valuable diamonds. She asks what he would do if the window is locked. He says he would go home and sleep. He says he has no interest in jewelry. She asks if he is going to steal some jewelry. She asks him to give up and admit who he is. She tells him to look at the diamond necklace she is wearing. She asks if he has ever had a better offer. He says he has never had a crazier one. During the fireworks he kisses her.
Later she is asleep on the couch, and he goes out on the balcony. She tells him to give back the jewels. He asks when it happened. She said it was when she was asleep. John asks Mrs. Stevens to let him look around. She is not worried because they are insured. John admits his name and says he was a jewel thief. He asks if they got everything, and she says yes. Frances comes in and tells her mother not to talk to him. John says he came in through the air shaft. Frances shows the list she found and gives it back to him. Mrs. Stevens says John is a real man, not like the ones Frances usually takes up with. Frances answers the door, and five men come in. John is on the roof escaping. Mrs. Stevens tells Frances that he is innocent until he is proven guilty. Frances says he is a thief.
John is fishing, and Hughson talks to him. John says someone is watching the Silva villa, and he wants to set a trap for him. John shows him a note he found. Hughson warns him he may be killed in the trap. Hughson offers to help, and John advises him not to be foolhardy.
That evening at the villa a man tries to strangle John. Another man has a wrench, and a man falls off the cliff and is killed.
Frances gets a newspaper and tells her mother that the cat burglar, John Froussard, is dead. In an office Hughson is prepared to pay off and asks if the recovery of the jewelry is imminent. John comes in and says Froussard had a wooden leg. John says the real cat will be at his funeral, and he wants to see him there.
At the funeral John observes the mourners, and Bertani walks over to him and speaks to him. He asks John about the American girl and advises him to marry her and go back to America. John says he will come to his restaurant. Daneille speaks in French and blames John, who slaps her and leaves. Frances calls to John from her car. He walks over, and she apologizes. John says Broussard was not the cat; but he was trying to kill him because he was getting too close to the cat. He suggests they go back to their mutual disregard. He asks her to pardon him. She says she won’t because she is in love with him. He says that is ridiculous, and words are playthings to her. They talk about going to a costume party. He asks her if she wants to see a real life burglary in action. She asks if it will be dangerous. He says it won’t be for tourists.
At an elegant costume party people applaud those arriving. Women wear fancy jewelry. Mrs. Stevens and Frances come in with John as a black slave behind them. Bertani drinks with the police commissioner. Mrs. Stevens asks John to fetch her pills for her, and he says he will. He comes back with them, and Frances asks him to dance. They continue to dance until no one else is. Then the orchestra stops playing. They walk out and go to her room. Hughson takes off his black mask and says her scheme has worked.
John is sitting on the roof. Someone is putting jewelry in a bag. John sees someone in black on the roof with a bag. He chases the person and finds it is Danielle. He says she always did her father’s leg work for him. Guns are fired at them. Frances tells them not to do that because he is not the cat. Danielle nearly falls off the roof but holds on with one hand. John takes her hand and tells her to say what she did and for whom. She says she did it for her father and that Bertani was behind it.
Two cars chase on the road. On the terrace Frances catches up with John. She says he needs the help of a woman, and he admits he is not a lone wolf. He takes her hand, pulls her to him, and kisses her. She says her mother will love it up there, and he gives her a second look.
This comedy distracts the audience with the plot about stealing jewelry while John and Frances spar with sexual tension and eventually find romance. They are both sought after because they are both wealthy, and like many Americans he admits that he does not give away his wealth. Yet he prefers the elegance of Europe to the crassness of Americans. Driving fast on a dangerous road provides a thrill, but ironically Grace Kelly would be killed years later on that road.