During the war against the Soviet Union from 1941 to 1945, the General Staff of the German Army received most of its information from an agent known in the Abwehr as "the Jew Klatt." The former Viennese real estate agent Richard Kauder worked under the alias Klatt as a double agent for the military intelligence of the Nazi regime to protect himself and his mother from persecution and murder. Both were considered "full Jews" under Nazi laws. Winfried Meyer describes the exciting life of Richard Kauder in its changing historical contexts, from the Austro-Hungarian monarchy to Cold War Austria. The comprehensive study is based on the files of various states' intelligence services. Among other things, it clarifies the origins of Klatt's legendary "Max" reports, which the German General Staff deemed crucial for the war and whose sources the Allied intelligence services searched for in vain well into the post-war period. The reports from the double agent Klatt remained "one of the greatest mysteries of the war" for them.