On the eve of the Anschluss, Prince Kurt von Rotenburg is preparing to leave his native Austria. While pausing for one last look at his favorite restaurant, the Café Weinergarten, Kurt encounters his old friend Professor Keller, the professor's daughter Marta and her fiancé, Wilhelm Erhardt. When Kurt and Marta fondly recall their childhood friendship, Wilhelm, a secret member of the Nazi party, becomes jealous and notifies the Gestapo that the prince is at the restaurant. After narrowly escaping the ensuing Nazi raid, the prince crosses the Czechoslovakian border and is reunited with the Kellers on a ship bound for America. Also aboard the vessel is Baron von Helsing, a covert Gestapo agent who feigns sympathy for the exiled prince while secretly working to spirit him back to Germany. As the prince and Marta begin to rekindle their childhood romance, the professor reminds his daughter of her pledge to marry Wilhelm, whom they believe has been incarcerated in a concentration camp. As the boat docks in New York, Marta, heeding her father's wishes, shuns Kurt. When the prince is besieged by a group of socialites led by the title- seeking Barbara Murdoch, Marta seizes the opportunity to depart without Kurt seeing her. Having fallen deeply in love with Marta, Kurt desperately searches for her. One day, while returning from a party with Barbara, Kurt spots Marta. After ordering his limousine to stop, Kurt jumps out and persuades Marta to allow him to drive her home. At the restaurant that Marta now runs with her father, Kurt finds a group of Austrian refugees, who criticize him for his frivolous life and for his neglect of his country and his people. When Kurt promises to help and pledges his support, they hand him a list of prisoners whose freedom they have been trying to win. The next day, Kurt receives an invitation to meet von Helsing at the German Travel Office. There, von Helsing promises to release all the prisoners on the list, including Wilhelm, if Kurt surrenders himself to Germany. Accepting von Helsing's terms, Kurt agrees to sail that night. Von Helsing leads Kurt to believe that he is sailing on a Belgium ship headed for Antwerp, when in reality the boat has been purchased by the Nazis and is destined for Hamburg. That evening, when Marta calls Kurt's hotel and learns that he has gone to the German Travel Office, she begins to suspect that something is amiss and hurries to the office herself. Bursting into the rooms, Marta is shocked to encounter Wilhelm. When Wilhelm boasts of his part in the ruse to trick Kurt into returning to Germany, Marta dashes to the boat to warn Kurt. After phoning the ship's captain to alert him of Marta's arrival, Wilhelm reaches for a gun and kills himself. Allowed to board the ship, Marta hurries to Kurt's stateroom and brokenly tells him that he has been tricked. When they try to leave the boat, they discover that the stateroom door has been locked, and they are now both prisoners bound for Germany. Later they are married by the sympathetic Belgium captain and resign themselves to their grim fate. Soon after, a radiogram arrives, notifying the captain that England has declared war on Germany and ordering him to change his course. Resentful of his treatment by the Nazis, the captain destroys the message, sending the vessel into enemy waters. As the boat sails into British seas, shots from a British destroyer halt the boat, which is then boarded by English officers, who announce that England is at war with Germany. After seizing command of the German craft, the English crew sail Marta and Kurt to the safety of British soil.