On September 5, 1945, cipher clerk Igor Gouzenko severed ties with the Soviet Embassy in Ottawa, reporting to the Royal Canadian Mounted Police allegations of extensive Soviet espionage in North America, providing stolen documents detailing Soviet intelligence matters to back his claims. This action sent shockwaves through Washington, London, Moscow, and Ottawa, changing the course of the twentieth century. Using recently declassified FBI and Canadian RCMP files on the Gouzenko case, author and Cold War scholar Amy Knight sheds new light on the FBI's efforts to incriminate Alger Hiss and Harry Dexter White in order to discredit the Truman Administration. FBI chief J. Edgar Hoover seized upon Gouzenko's defection as a means through which to demonize the Soviets, distorting statements made by Gouzenko to stir up "spy fever" in the U.S., setting the McCarthy era into motion. Through the FBI files and interviews with several key players, Knight delves into Gouzenko's reasons for defecting and brilliantly connects these events to the strained relations between the Soviet Union and the West, marking the beginning of the Cold War.