One of the most notorious German spies of the twentieth century, Lothar Witzke lived a life that reads like a thriller. Convicted of espionage in 1918, he was the only German spy sentenced to death by the United States during World War I. After the war, he was pardoned by President Calvin Coolidge, only to be later accused of responsibility for one of the most spectacular acts of sabotage in US history: the Black Tom munitions depot explosion.

After being repatriated to Germany, Witzke lived in Latin America and China as a German expat and later joined the Nazi party. He ran espionage squads in Great Britain during World War II and became a prominent businessman in Hamburg after the war. He was killed in Hamburg in 1962, possibly by an East German agent as payback for suspected double agent work on behalf of the British.

With Citizen of the Shadows, the first full biography of Witzke, Paul Friedland and Robert Hornick trace Witzke's morally complicated life and show readers how an infamous spy thrived in the interwar years and after. They probe his trial, conviction, and pardon, and analyze whether Witzke was really involved in the Black Tom explosion. In doing so, the authors uncover that many of the details of Witzke's life—long assumed to be true—were lies.