As the United States developed the world's first nuclear weapons in secret, it was surprised at the speed in which the USSR was able to also develop such weapons, and that such developments would lead to an unprecedented arms race. The USSR was able to obtain all the nuclear discoveries made by scientists who worked on the top-secret Manhattan Project through a very unusual spy, Elizabeth Zaroubin. She managed to gain the trust of great researchers, such as Einstein, in a story comparable to some of the best spy novels ever written.