In the spring of 1945 the Allies arrested the physicists they believed had worked on the German nuclear programme during the war. Interned in an English country house owned by MI6, their conversations were secretly recorded. Operation Epsilon sought to determine how close Nazi Germany had come to building an atomic bomb. It was in this remote setting - Farm Hall, near Cambridge - that the German physicists first heard of the bombing of Hiroshima. August 6 1945 was night that changed the course of history. The terrible weapon that the Americans unleashed on Japan caused unprecedented destruction and loss of life. That the Allies had