Princess Maria, whose country has been invaded by the Nazis, lives with her uncle in exile in New York. Although Maria's uncle encourages her to marry Count Peter de Chandome, in the hope that she will produce a male heir, Maria does not like him. Worried by her lack of interest in life, Maria's uncle suggests a change of scene and books her under the name Mary Williams on an airplane flight to San Francisco. To overcome her fear of flying, Maria accidentally takes too many sleeping pills. Then, when bad flying conditions force the plane to return to New York, Maria cannot be awakened. Pilot Eddie O'Rourke offers to help her walk off the effects of the drugs, but a misguided café owner, thinking all she needs is a good night's sleep, puts another sleeping pill in her coffee, and Maria passes out. With the help of Jean, the wife of Eddie's co-pilot Dave, Eddie puts Maria to bed in his apartment. The next day, Maria wakes to find several notes from Eddie asking her to meet him at 2:00 in front of the building. Maria returns to her hotel and tells her uncle that she spent the night in the ladies lounge at the airport. That afternoon, when she meets Eddie, she is followed by a Secret Service man who reports her activities to her uncle. Eddie, believing Maria to be a common war refugee, offers to show her New York. When she suggests that they have an ordinary date instead, Eddie introduces her to Dave and Jean. While the two men play handball, Maria and Jean spend the afternoon in a women's first aid class. Maria is embarrassed to admit that she has no skills, but volunteers to let the women practice their bandaging techniques on her. Later, after the two couples dine in a Chinese restaurant, Eddie proposes marriage. At first, Maria turns him down, but he forces her to admit that she wants to marry him. Meanwhile, Maria's uncle checks into Eddie's background and is pleased to learn that he is one of nine boys and that his father was one of eleven boys. He telephones Maria's father and convinces him that marriage to an American would be beneficial to their country. He then broaches the subject to Maria, who is delighted with the idea. When Eddie learns the truth about Maria, he is stunned but pleased that she will marry him. The wedding is to take place at the White House, and Mr. Washburn of the State Department uses the train trip to Washington, D.C. to give Eddie a crash course in royal diplomacy. Eddie begins to chafe under the requirements, however, and when he discovers that he will have to renounce his U.S. citizenship to marry Maria, he rebels. At the White House, he begs Maria to marry him and live as an ordinary citizen, but she cannot easily give up her role. Later, realizing that she is enslaved to her position, Maria uses the President's little dog to carry a letter to the President asking him to use his authority to help them. As a result, Maria and Eddie are quietly married by a Supreme Court justice. When Eddie expresses his hope that the guard who acted as their witness will not get in trouble, Maria explains that the "guard" was the President.