In 1940, Sally Maitland (Anna Neagle) is forced to leave England, ostracised as a Nazi sympathiser by everyone including her well-to-do family. On the ship to Halifax, Nova Scotia, Canada, she is courted by Polish aristocrat Jan Orlock (Albert Lieven) and by awkward British Naval Intelligence Officer Lieutenant Commander Jimmy Garrick (Richard Greene). She shows herself somewhat more amenable to Orlock's advances, and agrees to meet his mother in Halifax. Once there, however, it becomes clear no one is really who they say they are.