Confundido com um agente secreto, de uma hora para outra o publicitário Roger Tornhill se vê envolvido numa complicada trama de espionagem, sendo acusado inclusive de assassinato. Enquanto tenta provar sua inocência, é perseguido tanto pela polícia como por agentes criminosos. O filme comprova toda a habilidade de Hitchcock para mesclar suspense e aventura
Cary Grant empresta seu charme para viver John Robie, também conhecido como 'Gato'. Célebre ex-ladrão de jóias, ele está na Riviera Francesa quando uma onda de roubos toma conta do balneário. O problema é que o ladrão utiliza-se do mesmo estilo dos assaltos de Robie. Convencido de que alguém quer incriminá-lo, ele dribla a polícia e tenta encontrar o impostor antes que vá parar atrás das grades. Mas antes precisa fazer com que a viúva rica acredite nele.
Cowboy Ross McEwen arrives in town. He asks the banker for a loan of $2000. When the banker asks about securing a loan that large, McEwen shows him his six-gun collateral. The banker hands over the money in exchange for an I.O.U., signed "Jefferson Davis". McEwen rides out of town and catches a train, but not before being bitten by a rattler. On the train, a nurse, Miss Hollister, tends to his wound. A posse searches the train, but McEwen manages to escape notice. However a mysterious Mexican has taken note of the cowboy, and that loudmouthed brat is still nosing around. Who will be the first to claim the reward for the robber's capture?
Questioned as a murder suspect, solid (but drunk) citizen Al Willis attacks his police questioners, is beaten, and swears vengeance against them. Next night, Lieut. Parks is murdered; Willis is the only suspect in the eyes of tough Chief Conroy, who pursues him doggedly despite lack of evidence. The obsessed Conroy is dismissed from the force, but continues to harass Willis, who flees to a sleazy town on the Mexican border. Of course, Conroy follows. But which is crazy, Conroy or Willis?