A brilliant scientist and an infamous spy, Klaus Fuchs was convicted of espionage by Britain in 1950 for handing over the designs of the plutonium bomb to the Russians, putting an end to America's nuclear hegemony and intensifying the Cold War. But, was Klaus Fuchs really as sinister as he has been portrayed? Using archives as well as intimate family correspondence, Nancy Thorndike Greenspan brings into sharp focus how Fuchs—a German-born Communist dedicated to peace— leaked vital information as a way of levelling the playing field of the world powers.