Loosely based on folkloric accounts of the real Onofrio del Grillo (who lived in the eighteenth century), this character plays a number of pranks, one even involving Pope Pius VII.

On one occasion, when he is arrested at a dinner with common criminals, he turns to the populace in a vulgar speech, claiming that his nobility allows him to do what he wants, and that they, being poor, are not worth anything.

While he is leaving command to check on the fidelity of a young plebeian lover of his, the French guards enter the Holy See to arrest the Pope.

Onofrio has personally few prejudices and quickly includes acquaintances from the new order within his circle, becoming friends with a young commander of the French regiment as well as more senior officers.

Due to the obtuseness of the Roman people the show proves a failure, but Onofrio takes the chance to start an affair with the beautiful and free spirited singer Olympia.

One night, while walking around the ruins of the Forum to find a suitable spot for sleeping together, they notice a drunken coalman who is a perfect sosia of the Marquis.