Pope Pius IX was forced to go to Gaeta, Kingdom of the Two Sicilies, in exile due to the advent of the Roman Republic.

In the house of the Marquis Arquati, a papal noble, live his son Eufemio, weak and shy, with his wife Cristina (who married him forced by the family), his daughter Giacinta and the servant-mistress Rosetta.

Cristina, a supporter of the republic, has become the lover of Captain Giovanni Livraghi, a Milanese revolutionary, who rushed to the aid of the republicans, and a great friend of the Barnabite friar Ugo Bassi, opposed to temporal power and supporter of the rights of the people, but always faithful to his mission as a priest.

After many clashes, the surviving republican patriots, defeated by foreign troops, leave Rome and head in disorder towards the north.

But Bassi and Livraghi are arrested and sentenced to death, while the woman tries in vain to save her lover, begging for pardon from a powerful prelate who is a friend of hers.