Columbia subject headings:
Harvard subject headings:
Espionage, Japanese--History--19th century.
Espionage--Japan--History--19th century.
Japan--History--Meiji period, 1868-1912.
Ninja--Japan--History--19th century.
Police--Japan--History--19th century.
Spies--Japan--Biography.
Princeton subject headings:
Espionage--Japan--History--19th century.
Japan--Politics and government--1868-1912.
Ninja--Japan--History--19th century.
Police--Japan--History--19th century.
Spies--Japan--Biography.