Guido Gurlino, head of the Pisan army, wants the Florentine Maddalena Pazzi, but she rejects him, in love with Vitelli, head of the Florentine armies. Gurlino then kidnaps young Giovanna and makes her his wife. When, during a duel, Vitelli is wounded, he will be healed by Giovanna, whom the Pisans call Monna Vanna and whom she worships as an angel for her kindness.