This article examines interwar intelligence activities in the Baltic Sea region through the NKVD/NKGB interrogations of high-ranking Estonian political police officers in 1940–1942. The study reflects critically on Soviet interrogation reports as historical sources, concurrently arguing that they are instrumental since the material of the Estonian political police was destroyed in 1939–40. New insights are provided into the use of agents, Estonian military intelligence targeting the Soviet Union, the role of Russian émigrés in MI6’s operations, Estonian, Finnish, and Latvian intelligence cooperation, and the use of a notable Baltic German agent in countering Nazi-German influence operations and Estonian far-right subversion.