The film is a 125-minute, black-and-white biography of French priest and diplomat Charles Maurice de Talleyrand-Périgord (1754–1838), who served for 50 years under five different French regimes: the Absolute Monarchy, the Revolution, the Consulate, the Empire, and the Constitutional Monarchy. Its title comes from one of the main historical nicknames for Talleyrand, that he shares with demon king Asmodeus and English poet Lord Byron.

A minister falls in love with a blind young woman he sheltered, but so does his son.