Desperate to avoid an arranged marriage, Princess Marie trades identities with her maid, Marietta (Jeanette MacDonald), and sets sail from France to New Orleans. While at sea, her ship is attacked by pirates who kill the crew and take the women ashore. Terrified, they are rescued at the last second by Captain Richard Warrington (Nelson Eddy) and his band of mercenaries. Worthington escorts the incognito princess to New Orleans and, in the process, falls in love with her.