A file of correspondence and memoranda concerning the investigation of the Corby case, in which the defection to Canada of Soviet embassy worker Igor Gouzenko revealed the existence of a Soviet espionage network in Canada. The documents in this file discuss the defection of Gouzenko; his revelations during interrogation, including that the Soviets were gaining access to U.S. nuclear secrets; attempts to discover what other information had been passed; joint Canadian-British-American debates on how to proceed with the investigation, and whether to make a public announcement; preparations for the arrest of the Soviet agents; discussion of whether it would be better to collect more information about the Soviet network before arresting its members; the discovery that the Soviets had already withdrawn many of their agents; problems with the limited interrogation resources available in Canada; and a draft statement about the case to be presented to the Canadian parliament.