One of the most important and controversial aspects of the history of World War II is the failure of the Germans to build an atomic bomb. Germany was the birthplace of modern physics; it possessed the raw materials and the industrial base; and it commanded key intellectual resources. What happened? This study tells of the interplay between science and espionage, morality and military necessity, and paranoia and cool logic that marked the German bomb programme and the Allied response to it. On the basis of interviews and intensive research, the author concludes that Werner Heisenberg, who was in charge of the German atomic effort, consciously obstructed the development of the bomb and, in a famous 1941 meeting in Copenhagen with his former mentor Neils Bohr, in effect sought to dissuade the Allies from their pursuit of the bomb.