Spring 1917 on the Western Front: how were the Allies to discover where the Germans were going to make their next push, which parts of the line they were reinforcing? In this first full account of an Allied spying operation behind enemy lines during the First World War, Morgan describes how British military intelligence set up its Paris office in 1917 and persuaded a Luxembourg woman of remarkable courage to return as a spy to her native country to watch over the crucial railway marshalling yards there. To join her they sent Albert Baschwitz Meau, one of the most dashing, brave and colourful characters of this or any other war, who was floated one dark night in spring 1918 in an unpowered balloon over German lines... Morgan reveals how the Allies recruited agents in Europe and ran their operations in enemy-controlled territory. But as well as the espionage story, she also tells the personal stories of the individual men and women who worked under such intense pressure and in such exceptional circumstances. This is one of the most significant, as well as one of the most exciting, contributions to the literature of the First World War for many years.