Michele Pezza is a brigand known as "Fra Diavolo" and fights with his "masses" in the mountains of Campania to drive the French out of the Kingdom of Naples.
Having succeeded, thanks to his courage and skill in both military and espionage, the new Neapolitan government lavishes him with honors and appoints him colonel of the regular army.
In the long run, however, in that idle life among the comforts and riches, he feels nostalgia for the adventurous existence he had always led.
Thanks to the intervention of Gabriella Del Prà, an influential lady sincerely in love with him though never reciprocated, his sentence is suspended on condition that he submit to the new French government.
On the journey to Naples, Fra Diavolo manages to escape with Gabriella's complicity and hides in the mountains of Calabria, entering into legend.