The Gouzenko Affair 1945-1946
The Gouzenko Affair brought the realities of the emerging Cold War to the attention of the Canadian public. On September 5, 1945, cipher officer Igor Gouzenko left the Soviet Embassy with more than 100 documents which exposed the existence of a Soviet spy ring in Canada with links to others in the United States and Great Britain. His allegations gave rise to the creation in 1946 of a Royal Commission of Inquiry known as the Kellock-Taschereau Commission. Its confirmation of the country's vulnerability convinced the federal government to strengthen Canada's national security system.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.