When Margaretha Zelle, a young woman living in The Hague, answers a lonely hearts advertisement she becomes drawn into a relationship with an army captain twice her age. After a hasty wedding, they depart for Indonesia, where the marriage collapses amid infidelity and violence. Seeking a new life, Margaretha returns to Europe and travels to Paris, where she adopts the stage name Mata Hari, reinventing herself as an exotic dancer. In her new role she attracts the attention of numerous admirers, many of whom are officers, ready to share their secrets with a woman of notorious allure and intrigue, as Europe lurches towards explosive conflict.