LEEUWARDEN, the Netherlands — In December 1915, Margaretha Zelle, the woman known to all the world as the exotic dancer Mata Hari, was traveling by ship from one of her lovers in Paris to another in The Hague. The international sex symbol was famous for provocative routines in a nude body stocking with a bejeweled bra and golden headdress. Sometimes she would tell people she was a Javanese princess or the daughter of an Indian temple dancer, but only rarely would she reveal that she was Dutch. It was the middle of World War I and her circuitous route took her through British waters, where the authorities stopped the boat to question those on board. After looking at Zelle’s papers, and searching her possessions, they made a note: No evidence of anything had been found on her person, but she was nevertheless a “bold sort of woman who is not above suspicion.” In the charged atmosphere of the war, this was enough for the authorities to call for her arrest if she ever tried to enter the United Kingdom again. A copy of their report was sent to the French secret service, where it landed on the desk of a French military intelligence officer, George Ladoux.