Nathalie Sergueiew had an alias, it was Treasure. Nathalie was a German spy, a German spy with a twist. A spy that was really working for the British Secret Service. The Abwehr believed that she was loyal but she was really feeding them info that had been prepared by the British. This info helped to mislead the Germans for almost three years from 1943 to 1945. The British felt that even though she was doing a good job for them that she was not fully committed and didn't display discretion in some of her actions.

One of the things that made this former journalist so valuable to the British was the fact that she spoke several languages fluently, and those languages included English, German and French. Nathalie Sergueiew was born in Russia in 1912 . She attended school in Paris then spent a few years traveling around Europe. As a journalist she had even interviewed Hermann Goering. Some say that she had become an admirer of the Nazis but when she was offered a job with them working in intelligence, in 1937, she quickly refused. She reversed her decision after the war started but only because she felt a loyalty to the allies and wanted to help them, she said.

Her spymaster, Emil Kilemann, had her educated in many different spy skills. She got herself stationed in England where she promptly contacted the authorities and offered her services to them as a double agent. This part differs with several people, some who say she contacted the British through their Embassy in Spain. She went on to become one of the most effective British Agents. She had left her dog with British dog handlers but when he died in their care Nathalie was irate and threatened to tell the Germans about the plans for the D-Day invasion. As we can all imagine, this must not have gone over too went with the British.

Nathalie Sergueiew had a supervisor in MI5, the British Intelligence Agency, named Mary Sherer. Ms. Sherer didn't care very much for her and warned her supervisors that she was "exceptionally temperamental and troublesome" and that they would have trouble with her.

The British always questioned any German agents that wanted to become double agents. An interesting fact that they learned from Nathalie Sergueiew was that she was taught a unique cipher based on a certain edition of a French novel. If you didn't have this book, you couldn't decode the message. This system was not unique but had been in use for many years before the second world war. The way it worked was a message would contain a series of numbers. These numbers would indicate page, paragraph and word. Using this system it was easy to build a message that could not be broken without knowledge of which book was used. The bible was one of the favorite books of spies for ciphering.

Nathalie Sergueiew had outlived her usefulness when she began to a secret signal with the Germans without telling her British Bosses. To make matters even worse, she had an affair with an American soldier and she admitted telling him everything about herself. This type of behavior could simply not be tolerated. She was beginning to put everyone at risk by her actions. She was let go by Colonel Robertson. She met with Mary Shereer the next day and gave her the secret signal code. She returned to France with the intention of publishing her memoirs and was calling her British handlers 'gangsters' and was not going to keep their identities secret in her book. She published the book in 1968 against the wishes of Colonel Robertson.

It seems her uncle was the head of the Association or Ex-serviceman in Russia and disappeared in 1937 in Paris. It is thought that he was gathering white russians together and that the KGB assassinated him. He was a close relative of General Wrangel who was the head of the white army that fought against the communists.