All the works included in this collection are devoted to the work of the intelligence services during the First World War and were written by employees of these services. For Basil Thomas, the head of the crime department at Scotland Yard during the First World War, there were almost no secrets that he was not privy to would be dedicated. During the four years of the war, he was in continuous contact with government officials from many countries. His book is dedicated to the secret side of the war. R. Bukar's book fascinatingly introduces the techniques and methods of work of the Allied intelligence services in the First World War. Louis Rivière dedicated his work to the work of the German secret service in Madrid.