This is the first biography of an intrepid young French woman, Lily Sergueiew, who led an adventurous life and became famous as one of the five D-Day spies. In 1939, her bicycle ride from Paris to Saigon was interrupted by the outbreak of war. Disgusted by the Fall of France in 1940, she took the courageous decision to personally help the Allies drive the Nazis out of France: she would get the Abwehr to train her as a spy and have herself sent to England. Once there, she would betray the Nazis and place herself at the disposal of the Allies. It took three emotionally exhausting years to achieve this. She arrived in England just in time to become TREASURE, one of the five spies who misled the Nazis into believing that the Allies would land in the Pas de Calais. This disinformation operation saved countless lives. But Lily found the English cold and ungenerous towards her. They knew that she had a fatal medical condition. She had also risked her life – and her parents’ lives – every day she worked for the Nazis, yet the English would not let her bring the dog who was such a comfort to her. They told her that her work was vital to their cause, but for Lily their behaviour meant that it was not worth a dog. So she hid from them that the Nazis had given her a control code to prove that her radio messages were genuine: it gave her a sense of power to know that she could destroy her work – and the whole D-Day deception – with a single keystroke. She did not intend to use it, but once she had revealed it, she was dismissed straight after D-Day. This meant that she could join the Free French Forces and be sent to France to care for Displaced Persons left in the wake of the retreating Nazis. Working with liberated prisoners from Buchenwald, she married the American Major in charge of the region who had fallen in love with her. He took her to America where he hoped that her condition could be cured. It could not, and she died (largely forgotten) with her husband at her side in 1950.