Information about the author of the book "I Was Stalin's Agent", available below, is provided here. This may help readers to better evaluate the contents of the book.
"Walter Germanovich Krivitsky (Ва́льтер Ге́рманович Криви́цкий; June 28, 1899 – February 10, 1941) was a Soviet intelligence officer who revealed plans of signing the Molotov–Ribbentrop Pact after he defected to the West.
Walter Krivitsky was born on June 28, 1899, to Jewish parents as Samuel Ginsberg in Podwołoczyska, Galicia, Austria-Hungary (now Pidvolochysk, Ukraine), he adopted the name "Krivitsky," which was based on the Slavic root for "crooked, twisted". It was a revolutionary nom de guerre when he entered the Cheka, Bolshevik security and intelligence service.
Krivitsky operated as an illegal resident spy, with false name and papers, in Germany, Poland, Czechoslovakia, Austria, Italy, and Hungary. He rose to the rank of control officer. He is credited with organising industrial sabotage, stealing plans for submarines and planes, intercepting correspondence between Nazi Germany and Imperial Japan, and recruiting many agents, including Magda Lupescu ("Madame Lepescu") and Noel Field.
In May 1937, Krivitsky was sent to The Hague, Netherlands, to operate as the rezident (regional control officer), operating under the cover of an antiquarian. There he co-ordinated intelligence operations throughout Western Europe.
At the time, the General Staff of the Red Army was undergoing the Great Purge in Moscow, which Krivitsky and close friend, Ignace Reiss, both abroad, found deeply disturbing. Reiss wanted to defect, but Krivitsky repeatedly held back. Finally, Reiss defected, as he announced in a defiant letter to Moscow. His assassination, in Switzerland, in September 1937 prompted Krivitsky to defect the following month.
In Paris, Krivitsky began to write articles and made contact with Lev Sedov, Trotsky's son, and the Trotskyists. There, he also met undercover Soviet spy Mark Zborowski, known as "Etienne," whom Sedov had sent to protect him. Sedov died mysteriously in February 1938, but Krivitsky eluded attempts to kill or kidnap him in France, including flight to Hyères.
As a result of Krivitsky's debriefing, the British were able to arrest John Herbert King, a cypher clerk in the Foreign Office. He also gave a vague description of two other Soviet spies, Donald Maclean and John Cairncross but without enough detail to enable their arrest. The Soviet intelligence operation in the United Kingdom was thrown into disarray for a time.
At the end of 1938, anticipating the Nazi conquest of Europe, Krivitsky sailed from France to the United States. Krivitsky did not stop with defection; he went on to become an anti-Stalinist.
With the help of journalist Isaac Don Levine and literary agent Paul Wohl, Krivitsky produced an inside account of Stalin's underhanded methods. It appeared in book form as In Stalin's Secret Service (UK title: I Was Stalin's Agent), published on November 15, 1939, after appearing first in sensational serial form in April 1939 in the top magazine of the time, the Saturday Evening Post. (The title had appeared as a phrase in an article written by Reiss's wife on the first anniversary of her husband's assassination: "Reiss... had been in Stalin's secret service for many years and knew what fate to expect.") The book received a tepid review by the very influential New York Times. Attacked by the American left, Krivitsky was vindicated when the German-Soviet Nonaggression Pact, which he had predicted, was signed in August 1939."
(from Wikipedia)