Columbia subject headings:
Communism--Soviet Union--History.
Secret service--Soviet Union--History.
Spies--Soviet Union--History--20th century.
Harvard subject headings:
Communism--Soviet Union--History
Secret service--Soviet Union--History--20th century.
Spies--Soviet Union--History--20th century.
Princeton subject headings:
Espionage, Soviet.
Spies--Soviet Union.