When Elizabeth Bentley slunk into an FBI field office in 1945, she was thinking only of saving herself from NKGB assassins who were hot on her trail. She had no idea that she was about to start the greatest Red Scare in US history. Bentley was a Connecticut Yankee and Vassar graduate who spied for the Soviet Union for seven years. She met with dozens of highly placed American agents who worked for the Soviets, gathering their secrets and stuffing sensitive documents into her knitting bag. But her Soviet spymasters suspected her of disloyalty - and even began plotting to silence her for ever. To save her own life, Bentley decided to betray her friends and comrades to the FBI. Her defection effectively shut down Soviet espionage in the US for years. Despite her crucial role in the cultural and political history of the early Cold War, Bentley has long been overlooked or underestimated by historians. Now, new documents from Russian and American archives make it possible to assess the veracity of her allegations. This biography rescues Elizabeth Bentley from obscurity and tells her dramatic life story.