When the Germans invade Czechoslovakia, a scientist (James Harcourt) flees to England, but his daughter Anna (Margaret Lockwood) is arrested. She escapes from a camp with the aid of a fellow prisoner (Paul Henreid), but the Gestapo follows and manages to capture her and her father. British Secret Service Agent Dickie Randall (Rex Harrison) heads after them, disguised as a senior German Army officer.