This is a history of the Norwegian Intelligence Service (NIS) during the Cold War, based on its secret archives. The author presents detailed descriptions of the build-up of a network of Norwegian signals intelligence stations in the north; border crossings by clandestine agents; the reporting of Norwegian merchant mariners from ports behind the Iron Curtain; the intimate co-operation between the NIS and the secret services of the United States and other countries; as well as the establishment of a stay behind network.