Ventriloquist Jerry Morgan has failed with another love affair. The reason: when the relationship reaches the point when it is time to discuss marriage, his doll Clarence becomes mean and jealous. His fiancTe Audrey leaves him and Jerry smashes his two dolls, Clarence and Terrence. Morgan's dollmaker Papinek is member of a spy ring who has stolen the secret plans to the top secret Lafayette airplane. Since Morgan is leaving for Zurich the same night, he decides to use Morgan's dolls as a mailbox and hides the secret plan in the heads of the dolls. Another secret spy ring also wants to get their hands on Jerry's luggage and they *also* follow him. Eventually, Jerry is chased by both these organizations as well as the police, who suspects him of murder.

On his last night performing in Paris, American ventriloquist Jerry Morgan insults his fiancée, ballerina Audrey Wood, through his dummy Clarence, then insists that he had nothing to do with it. Fed up with Jerry's hostile, neurotic behavior, Audrey ends their engagement and leaves for London, prompting Jerry to slam Clarence onto his dressing room floor. Jerry's longtime manager, Marty Brown, witnesses the attack and announces that he is quitting unless Jerry gets psychiatric help. Though apprehensive, Jerry agrees to fly to Zurich to see Dr. Kreuger and takes the broken Clarence and his twin dummy Terence to Maurice Papinek's repair shop. At the same time, secret agent Brodnik steals the blueprints for two French-built weapons known as "Lafayette X.V.27" and eludes the police long enough to deliver them to his contact, Papinek. Papinek, who is patching up Clarence and Terence, stuffs the blueprints inside the dummies' heads and instructs Brodnik to call Lazlo Gromek in Zurich about retrieving the documents. While sneaking home, Brodnik is shot by police but, before expiring, calls Gromek and reveals that the blueprints are arriving in Zurich with a "redheaded ventriloquist." Unknown to Brodnik, the call has been overheard by agents representing master spy Godfrey Langston, an aristocratic but amoral Englishman. After the agents inform Langston about Brodnik's conversation, Langston deduces that the ventriloquist must be Jerry and arranges to fly to Zurich with him. During the flight, Jerry, who is nervous about seeing Kreuger, irritates fellow passenger Ilse Nordstrom with his oafishness, then acts baffled when Langston, who assumes that Jerry is a rival agent, calls him to his side and obliquely discusses buying the documents from him. At both the London airport and the hotel, Gromek tries to make contact with Jerry by whispering his own name, but the American assumes that "Gromek" means thank you in German and dismisses him. In the middle of the night, Jerry is half-awakened by hissing radiators and stumbles into a neighboring suite, thinking it is Marty's. Jerry falls asleep in the nearest vacant bed, only to discover the next morning that he is in Ilse's room. After Ilse throws him out, Jerry accidentally enters the women's bathroom and unknowingly showers in the stall next to Ilse's. Upon being discovered by an irate Ilse, Jerry stammers more apologies, then encounters Gromek in the hallway. When Gromek suddenly mentions Papinek, Jerry tells him about the condition of his dummies, giving Gromek an idea. Sometime later, Gromek sneaks into Jerry's room, removes the blueprint from Clarence and leaves, unaware of the second blueprint's existence. At the same time, Langston learns about Gromek and Papinek and plots to steal the blueprints from Jerry. At his office, Dr. Kreuger, meanwhile, introduces Jerry to his psychiatric colleague, who turns out to be Ilse. Ignoring his flirtations, Ilse injects Jerry with truth serum and listens as he describes how his parents' frequent fights upset him, and their vaudeville act entranced him. After Ilse concludes that Jerry's fear of marriage stems from his unhappy childhood, Kreuger declares that Jerry must go with Ilse to London to continue his treatment. Ilse and Jerry fly to London on Langston's private plane, and Jerry continues to be impressed by Langston's apparent kindnesses. Later, during his first session with Ilse, Jerry notices a photograph of an American officer on her desk and jealously begins questioning her about it. Ilse admits that the officer was her sweetheart and was killed in combat, then kicks Jerry out. The next day, however, he follows her around town and confronts her about the guilt she feels for surviving the war. Jerry's astute assumptions melt Ilse's resistance, and they end up in each other's arms. Meanwhile, Gromek and Papinek, both of whom have flown to London, meet at Gromek's hotel, where Papinek orders Gromek to retrieve the other blueprint. Gromek enters Jerry's hotel room at the same time as one of Langston's agents, and after tossing a knife into the agent, Gromek shoves the body into a closet and hides when Jerry walks in. Bubbling with love, Jerry soon heads over to Marty's room, and during his absence, Gromek tears apart the dummies. Gromek then is interrupted by the arrival of another Langston spy, who forces him at knifepoint to telephone Papinek and make arrangements to turn over the second blueprint. Moments later, Jerry returns and, upon discovering the first agent dead in the closet, runs for the police after pocketing Gromek's dropped room key. While hysterically trying to explain things to the police, Jerry opens another closet door, and Gromek's body falls out. Suspected of both crimes, Jerry flees the police, ending up in a pub, where a group of Irishmen are having a party. To blend in, Jerry pretends to be Irish and soon passes out with drink. Finding Gromek's room key in Jerry's pocket, the Irishmen take him to Gromek's hotel. The following afternoon, Jerry, unaware that Chief Inspector Wilton is with her, phones Ilse, who agrees to come to the hotel. Jerry hides his face when the hotel clerk brings him some food, but his cover is blown as soon as he opens the closet and Papinek's body tumbles out. Jerry again flees, ending up at a car dealership, where he impersonates both a customer and a salesman and steals a sports car. Ilse, meanwhile, tells Wilton that Jerry will probably go to Langston's, and Langston is notified. As predicted, Jerry races to Langston's estate, but is grabbed as soon as he arrives. Jerry breaks free and hides under a table just as Langston and Brutchik, the spy to whom Langston is selling the blueprints, sit down to discuss the transaction. Jerry eavesdrops until his presence is discovered, but manages to escape by throwing his voice and impersonating the police. In the sports car, Jerry tears back to town and takes refuge in a theater where Audrey is about to perform a ballet. To elude the police, who have been summoned by a frightened Audrey, Jerry dons a costume and joins the other dancers on stage. When Langston's men try to kill him from the wings, however, Jerry gives himself up, but implicates Langston as a murderous spy. Wilton refuses to consider his claims until Langston inadvertently reveals the weapon's secret name. Wilton arrests Langston, and later, a just married Jerry and Ilse look forward to a happy, sane honeymoon.