In 1942, with a black-market chicken tucked under his arm by his mother, Leo Marks left his father's famous bookshop, 84 Charing Cross Road, and went off to fight the war. He was twenty-two. Soon recognized as a cryptographer of genius, he became head of communications at the Special Operations Executive (SOE), where he revolutionized the codemaking techniques of the Allies and trained some of the most famous agents dropped into occupied Europe. As a top codemaker, Marks had a unique perspective on one of the most fascinating and, until now, little-known aspects of the Second World War. This memoir provides a unique inside picture of the extraordinary SOE organization at work and reveals for the first time many unknown truths about the conduct of the war. Between Silk and Cyanide chronicles Marks's obsessive quest to improve the security of agents' codes and how this crusade led to his involvement in some of the war's most dramatic and secret operations. Among the astonishing revelations is his account of the code war between SOE and the Germans in Holland. He also reveals for the first time how SOE fooled the Germans into thinking that a secret army was operating in the Fatherland itself, and how and why he broke the code that General de Gaulle insisted be available only to the Free French.