When the Nazis take Prague, Dr. Bomasch (James Harcourt) escapes, but his daughter, Anna (Margaret Lockwood), is taken to a concentration camp. There she meets Karl (Paul Henreid), a Czech man who helps her escape. She flees with Karl to England where her father is already working for the Royal Navy, guarded by undercover agent Dickie Randall (Rex Harrison). No sooner are they reunited when Karl, actually an SS agent, steals father and daughter back to Germany. It is up to Randall to save them.