Following the defection of Soviet cipher clerk Igor Gouzenko in 1945, Canada was stunned by the alarming revelation that some of its own citizens were engaged in espionage for the Soviet Union. This research explores how the Canadian government utilized the controversial Kellock-Taschereau Commission—sometimes judiciously and at other times recklessly—to uncover and eliminate domestic spies during the early Cold War period. Drawing on a diverse range of sources, including the Commission’s comprehensive records, GRU documents supplied by Gouzenko, American Venona decryptions, Soviet KGB archives, and recently declassified files from British MI5 and MI6, authors Reinhold Kramer and Tom Mitchell offer a detailed account of the crisis. They reveal that, despite certain errors concerning civil liberties, the government's suspicions were largely justified. The book intricately weaves together the evidence against the spies, the tactics of Soviet espionage, the complex legal challenges encountered by the state, and the resulting political fallout. With access to hundreds of newly released British intelligence documents, this study provides both experts and general readers with fresh insights into the espionage crisis of 1945–46 and its significant role in exposing Canada’s postwar security and intelligence vulnerabilities.