Act 3 "Infamy!"Scene 1: The Basilica of Sant' Ambrogio.In the subterranean vaults of the Basilica, Arrigo is inducted into the Knights of Death, warriors who have pledged to fight to the death rather than suffer defeat or imprisonment. All unite to swear an oath to support the cause of Italy (Giuriam d'Italia por fine ai danni / "We swear to put an end to Italy's wrongs") and to drive the foreign forces back across the Alps.Scene 2: Rolando's castle.Lida has heard that Arrigo has joined the Knights of Death, and desperately tries to contact him via a note to be conveyed by her maid, Imelda. As Imelda is about to leave, Rolando suddenly enters to say farewell to Lida and to their son, whom he has brought to him. Imelda hides the note, then quickly leaves. Rolando tells Lida to convey his love of country to their son, and to bring the boy up to love the fatherland (Digli ch'è sangue italico / "Tell him he is of Italian blood").Arrigo enters, summoned by Rolando, who does not know that his friend has joined the Knights of Death. Thinking that Arrigo has been ordered to remain to guard Milan, Rolando begs him to take care of his wife and son in the event of his death (Se al nuovo dì pugnando /"If when we fight on the morrow"). The two men part company, Rolando moved by grief, Arrigo with embarrassment. Just as Rolando is about to leave, Marcovaldo delays him, telling him that his honour has been betrayed and presents him with Lida's note to Arrigo, which he has intercepted. Rolando is enraged and proclaims that he will obtain double vengeance on his wife and his friend (Mi scoppa il cor / "My heart is bursting").Scene 3: A room in the tower.Having received no response to her note, Lida goes to see Arrigo in his room in the tower, where he is writing a farewell letter to his mother. Although they declare their love for each other, he tells her that he has not received any note. Lida tries to persuade him to abandon his suicidal quest while he distraughtly recounts his dismay at finding her married. Finally, Lida says that they must separate for the sake of her husband and child. Then Rolando is heard at the door and, before he enters, Lida hides on the balcony.Rolando confronts Arrigo, telling him that he now knows about his vow to the Knights of Death and encourages him to depart. Then he opens the balcony door and discovers Lida. Rolando is in a rage while Arrigo confesses his love for Lida but asks for death. Lida then declares that she is the guilty one. Still raging, Rolando storms out to lead the Milanese troops into battle, but as he leaves, he locks the tower door on Arrigo and Lida, declaring that Arrigo will suffer a fate worse than death: the infamy of being absent from the battle in which he had promised to fight, and so will lose his honour. As trumpets signal the beginning of the battle, Arrigo, in desperation, leaps from the tower into the moat, shouting "Long Live Italy!". Lida remains in anguish.