Act I. Revenge. The story takes place in the years 1095 to 1097. Pagano, jealous of his brother Arvino, had tried to kill him the very day of his marriage to Viclinda, and has been exiled.
Many years later he returns to Milan playing the role of the penitent, and the two are reconciled. In reality, he begins to scheme against his brother through Pirro. A group of cut-throats is hired. But Arvino senses danger and prepares to fight the dark menace approaching.
The night of the attack, darkness. Pagano strikes someone with his sword: it is his father. Desperately, he tries to kill himself, but is arrested.
Act II. The caveman. In Antioch, the tyrant Acciano prays to Allah to unleash his ire on the crusaders. His son Oronte is in love with a Christian prisoner, Giselda, daughter of Arvino and Viclinda, and wants to convert to Christianity, as his mother Sofia has already secretly done. In the meantime Pirro arrives near the city and goes to Pagano, who lives in a cave as a hermit in expiation of his past wrongdoing.
Pagano declares his readiness to guide the crusaders into the infidel's city. When he realises that they are Lombards, Pagano arms himself as well.
In the harem. Sofia tells Giselda that Acciano and Oronte have been killed: the young girl cries out against an unjust god who could permit war, and Arvino, arriving in time to hear this, threatens to kill the impious girl: theirs is a holy war. The saintly hermit, unrecognised, saves her: "Evidently the poor girl is mad," he says.
Act III. Conversion. Oronte is not dead: wounded and disguised as a crusader, he finds Giselda in the Valley of Josafath. The two promise each other eternal love. They must flee, because Arvino, who has found out about their love, is looking for them to separate them; he has also heard that Pagano is nearby, and proposes to find him and punish him for once and for all. Oronte and Giselda find shelter in the hermit's cave. Here the wounded man is baptised, and dies in the arms of his beloved.
Act IV. The Holy Sepulchre. Giselda has a vision: Oronte appears to her and tells her that the crusaders will find water in the desert. The crusaders are suffering badly from thirst, but miraculously, the fountain of Siloe starts gushing water.
The battle continues, and the hermit is mortally wounded. Taken to Arvino's tent, he reveals his identity as Pagano. The crusader commander pardons him and carries him to the entrance of the tent from where he can see the Christian banner already flying over Jerusalem.
The fourth of Verdi's opera written for the Scala Theatre and thoroughly Milanese from the title to the author of the subject, Tommaso Grossi. Temistocle Solera wrote the libretto.
A drama on a religious theme, full of processions, prayers, a baptism and naturally a crusade: the clerical authorities were suspicious and asked the administrators of justice to investigate. Chief of police Torresani, after reading the libretto, ordered a few changes: for instance, in the theatre the Ave Maria could not be sung, since the theatre was not an appropriate place for a prayer; Verdi unwillingly had to change the aria to a Salve Maria. With these small modifications, the opera was ready, and was first performed at the Scala on February 1st, 1843. It was also staged in Senigallia that summer and in Venice the following winter.
The original opera score has a dedication by Verdi to Maria Luigia of Habsburg, Duchess of Parma, the birthplace of the Maestro.