Unabashed British wartime propaganda starring Henreid as a Nazi spy who sneaks into England and is taken in by the kindly unsuspecting Gwenn and his family. From there he is able to establish radio contact with the Nazis, so that he can pinpoint British targets for German planes and
paratroopers. To complicate matters, von Hernried starts a romance with Gwenn's unsuspecting daughter Maguire. Gwenn kills a German officer when the attack starts and is taken out and shot just as British bombers arrive to blow up the whole house.