When only six of eight would-be German saboteurs are sentenced to death by an American court during World War II, an FBI agent complains to his boss, Craig (Ward Bond), about the other two.

When Carl attends a Bund meeting, his colleague Ernst Reiter divulges that he has been called back to Germany to be trained as a saboteur.

Later, Colonel Taeger (Dennis Hoey) informs him that Helga is suspected of being in the German Underground, and orders him to continue seeing her to find incriminating evidence.

When Carl's father becomes seriously ill, Craig tells him about his son's real mission, but stresses he can divulge the information to no one, not even his wife.

Because of his excellent performance at the sabotage school, Carl is put in charge of the first group of saboteurs to be sent to America after the United States enters the war.

The submarine is attacked by American bombers, but escapes unharmed, and the saboteurs depart in a life raft before Taeger's message is received.