The book describes the activities of the World Party of Communists (Comintern), which existed in 1919-1943. At the same time, the author paid main attention to its secret side, about which nothing has been published in Russian until now. The author, the youngest son of I.A. (Osip) Pyatnitsky, the head of the apparatus of the Comintern in 1921-1937, built a narrative through a presentation of the main events of the biography of his father. He paid significant attention to the story of how I.V. Stalin established the regime of personal power in the party and in the country, how he physically destroyed almost all Bolshevik-Leninists, including I.A. Pyatnitsky, who spoke out against mass repressions in the USSR. The book was written based on archive materials, memoirs of participants in long-standing events, press materials of the 1920s and 30s. It is intended not only for professional historians, but also for a wide range of readers interested in the history of the 20th century.