In Czechoslovakia, inventor Axel Bomasch () flees the country moments before the Nazis invade in 1939 to take him into custody to create war weapons for the German onslaught against the world. Unfortunately his daughter Anna () is captured and put into a concentration camp as a medical nurse. When Anna witnesses the beating of fellow inmate Karl Marsen (Paul Henreid) at the hands of German soldiers she forms an immediate alliance with the man. After learning that she is Alex Bomasch's daughter and that she wants to get to Switzerland, Karl devises a plan to get them both out and into England where they manage to get to a safe house. Anna receives a message that to find her father she should go seek out Gus Bennett () an effeminate singer and salesman of popular songs. Bennett is a British Intelligence agent working undercover and is suspicious that Anna was able to escape from Germany so easily. His suspicions are well-founded when he realizes that Karl has planned things to get Anna out of Germany in order to find the location of her father Alex so that Germany can spirit him back to the fatherland. Bennett goes undercover as a German officer to get back to Germany when Anna is kidnapped with her father and taken back to Munich by Karl. Along the way Bennett is found out and discovers that he must incorporate the efforts of Charters() and Caldicott () whom he has known since his college days. A tense game of cat-and-mouse ensues as Bennett attempts to get Anna and Alex back to England before being found out.