[1]The U.S. has not yet entered World War II when kindly stamp dealer Otto Becker (Conrad Veidt) is unexpectedly visited by his twin brother, Baron Hugo von Detner, the new German consul to the U.S. and one of the leaders of a spy ring engaged in sabotage.

Meanwhile, as he continues to pass as von Detner, Becker starts feeding what he learns about the spy ring's operations to the police via anonymous telephone calls.

Aware now of Becker's true identity and the fact that he was the informant, Richten threatens to punish him by notifying the authorities that De Relle is a spy.

Principal photography on Nazi Agent began in early November 1941 and ended on December 16, 1941, after the attack on Pearl Harbor and Germany's declaration of war against the United States.

Mr. Veidt as a simple, unpretentious and loyal naturalized American is coerced by his twin, a Nazi consul, into assisting with some spy activities.