Frenchwoman Nathalie Sergueiew, alias "Treasure", was one of many agents who double-crossed the Germans during WW2. In Berlin she was taught espionage skills such as secret ink writing, ciphers and radio telegraphy. However, she was secretly opposed to the Nazis. She reached Britain via Spain in 1943 and from then on her contacts in the Abwehr believed her to be loyally spying on the British for them. In reality, she was sending them deliberately misleading messages composed by MI5.
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