He wrote a polite letter to the U.S. Chemical Warfare Service asking for classified gas mask blueprints, promised they would stay with a good patriotic citizen, and the military mailed them to him. A week later they were in Berlin. This episode traces the life of Frederick Fritz Duquesne, the South African Boer War captain whose hatred of the British Empire drove him through prisons on multiple continents, sabotage of British ships in World War I, and finally the construction of the 33-person Duquesne spy ring in New York.

We look at how a naturalized citizen embedded himself in the pro-Nazi Order of 76 and even worked for the Works Progress Administration, how Admiral Canaris reactivated him in 1937, and how ordinary cooks, stewards and inspectors stole America’s most guarded technology. Herman Lang traced Norden bombsight blueprints at his kitchen table and smuggled them out in an umbrella handle. Then we follow William Sebold, the blackmailed radio operator who turned FBI double agent, the shortwave station on Long Island run by federal agents, and the surveillance that finally brought the ring down.

• How Duquesne escaped British, Portuguese and American custody and claimed credit for sinking HMS Hampshire
• Why espionage depends on access, not tuxedos, and how a Pan Am steward became a 24-hour courier
• The FBI agent who drilled through his own floor to plant a microphone above Duquesne’s apartment
• The subway and revolving-door evasion tactics of a spy who never saw the double agent in his own network
• How the roundup dealt what a German spymaster called the death blow to Nazi espionage in America