Columbia subject headings:
Spies--Europe--Biography.
World War, 1914-1918--Secret service--Germany.
Harvard subject headings:
Spies--Europe--Biography.
World War, 1914-1918--Secret service--Germany
Princeton subject headings:
Mata Hari, 1876-1917.
Spies--France--Biography.
Spies--Germany--Biography.
World War, 1914-1918--Secret service--Germany.