What is supposed to have happened before the curtain goes up on the opera is as follows: The old Count di Luna, sometime deceased, had two sons nearly of the same age. One night, when they still were infants, and asleep, in a nurse's charge in an apartment in the old Count's castle, a gypsy hag, having gained stealthy entrance into the chamber, was discovered leaning over the cradle of the younger child, Garzia. Though she was instantly driven away, the child's health began to fail and she was believed to have bewitched it. She was pursued, apprehended and burned alive at the stake.
Her daughter, Azucena, at that time a young gypsy woman with a child of her own in her arms, was a witness to the death of her mother, which she swore to avenge. During the following night she stole into the castle, snatched the younger child of the Count di Luna from its cradle, and hurried back to the scene of execution, intending to throw the baby boy into the flames that still raged over the spot where they had consumed her mother. Almost bereft of her senses, however, by her memory of the horrible scene she had witnessed, she seized and hurled into the flames her own child, instead of the young Count (thus preserving, with an almost supernatural instinct for opera, the baby that was destined to grow up into a tenor with a voice high enough to sing "Di quella pira").
Thwarted for the moment in her vengeance, Azucena was not to be completely baffled. With the infant Count in her arms she fled and rejoined her tribe, entrusting her secret to no one, but bringing him up—Manrico, the Troubadour—as her own son; and always with the thought that through him she might wreak vengeance upon his own kindred.
When the opera opens, Manrico has grown up; she has become old and wrinkled, but is still unrelenting in her quest of vengeance. The old Count has died, leaving the elder son, Count di Luna of the opera, sole heir to his title and possessions, but always doubting the death of the younger, despite the heap of infant's bones found among the ashes about the stake.
"After this preliminary knowledge," quaintly says the English libretto, "we now come to the actual business of the piece." Each of the four acts of this "piece" has a title: Act I, "Il Duello" (The Duel); Act II, "La Gitana" (The Gypsy); Act III, "Il Figlio della Zingara" (The Gypsy's Son); Act IV, "Il Supplizio" (The Penalty).
Act I. Atrium of the palace of Aliaferia, with a door leading to the apartments of the Count di Luna. Ferrando, the captain of the guard, and retainers, are reclining near the door. Armed men are standing guard in the background. It is night. The men are on guard because Count di Luna desires to apprehend a minstrel knight, a troubadour, who has been heard on several occasions to be serenading from the palace garden, the Duchess Leonora, for whom a deep, but unrequited passion sways the Count.
Weary of the watch, the retainers beg Ferrando to tell them the story of the Count's brother, the stolen child. This Ferrando proceeds to do in the ballad, "Abbietta zingara" (Sat there a gypsy hag).
Ferrando's gruesome ballad and the comments of the horror-stricken chorus dominate the opening of the opera. The scene is an unusually effective one for a subordinate character like Ferrando. But in "Il Trovatore" Verdi is lavish with his melodies—more so, perhaps, than in any of his other operas.
The scene changes to the gardens of the palace. On one side a flight of marble steps leads to Leonora's apartment. Heavy clouds obscure the moon. Leonora and Inez are in the garden. From the confidante's questions and Leonora's answers it is gathered that Leonora is enamoured of an unknown but valiant knight who, lately entering a tourney, won all contests and was crowned victor by her hand. She knows her love is requited, for at night she has heard her Troubadour singing below her window. In the course of this narrative Leonora has two solos. The first of these is the romantic "Tacea la notte placida" (The night calmly and peacefully in beauty seemed reposing).