The memo landed on Kim Philby's desk in Washington, DC, in July 1950. Three months later, Bruno Pontecorvo, a physicist at Harwell, Britain's atomic energy lab, disappeared without a trace. When he re-surfaced six years later, he was on the other side of the Iron Curtain. One of the most brilliant scientists of his generation, Pontecorvo was privy to many secrets: he had worked on the Anglo-Canadian arm of the Manhattan Project, and quietly discovered a way to find the uranium coveted by nuclear powers. Yet when he disappeared MI5 insisted he was not a threat. Now, based on unprecedented access to archives, letters and surviving family members and scientists, award-winning writer and physics professor Frank Close pieces together an answer to whether Pontecorvo's defection did indeed bring an end to a life of spycraft -and exposes the truth of a man irrevocably marked by the advent of the atomic age and the Cold War.