On the 29th of August 1949, the USSR set off their first atomic bomb, just four years after the Americans. The speed with which they achieved this surprised the world. What nobody knew was that it was the result of espionage implemented at the heart of the United States. Stalin was able to obtain all the nuclear discoveries made by scientists who worked on the famous Manhattan Plan. At the centre of the operation was a very unusual female spy, Elizabeth Zaroubin.