In 2000, boxes containing top-secret files were found in a shed. They detailed the lives and code names of Britain's first female agents during WWII. The spymistress, Vera Atkins, had committed treason by keeping the papers, but she had a reason for doing so. Vera was put in charge of the female spies, and when many of them went missing during the war, never to return, she was determined to find out their fate - in defiance of the British authorities.