During the Nazi uprising in 1939, they have captured prominent Czechoslovakian scientist Axel Bomasch and his adult daughter Anna Bomasch. Despite the senior Bomasch having escaped to England before the Nazis invaded Czechoslovakia, the Nazis were able to discover his hiding location in part due to an elaborate ruse using Anna, who at the time was imprisoned in a concentration camp, and Karl Marsen, a Gestapo officer posing as a fellow camp prisoner. Dickie Randall, an English officer using the code name Gus Bennett, decides to mount his own rescue of the Bomasches posing as a S.S. major.