A first generation American of German heritage becomes embittered at the loss of a brother in World War One. Moving to Germany to live with his grandparents, he becomes enthralled with National Socialism and willingly becomes an agent of the Abwehr. Returning to the United States, he pursues espionage against the United States on behalf of Nazi Germany.

The story details his efforts, his love affair, and eventually the investigation that will lead to him. The climax takes place on the interned French luxury liner Normandie and provides an alternative reason for the loss of that ship.