Columbia subject headings:
Espionage--Bulgaria--History--20th century.
Espionage--France--History--20th century.
Espionage--Soviet Union--History--20th century.
Kostov, Vladimir.
Spies--Bulgaria--Biography.
Harvard subject headings:
Espionage--Bulgaria--History--20th century.
Espionage--France--History--20th century.
Espionage--Soviet Union--History--20th century.
Kostov, Vladimir.
Spies--Bulgaria--Biography.
Princeton subject headings:
Espionage--Bulgaria--History--20th century.
Espionage--France--History--20th century.
Espionage--Soviet Union--History--20th century.
Kostov, Vladimir.
Spies--Bulgaria--Biography.