Angela Orsini and Massimo Colonna, the two representatives of the noble families, love and marry in secret, but during the ceremony Angela's father bursts in and challenges Massimo to a duel.
The latter juggles to avoid the clash, but a dagger thrown by a hitman of Tancredi Serra who demands the hand of Angela, kills the old Orsini.
Massimo is forced to flee Rome, but returns there after the city is besieged, and before going to fight he makes a peace agreement with the Orsini to prove his innocence and love for Angela.
The leader of the resistance, Massimo, then manages to break the circle of the besiegers thanks to the help of a certain Fanfulla from Lodi, freeing the defenders.
Meanwhile, Angela learns from the assassin, now dying, the true version of the killing of her father: now nothing can prevent the marriage between her and Massimo.