In Rome, Monticelso quizzes Francisco about his plans following Isabella’s death by poisoning. Francisco does not want to go to war with Bracciano because any such war would bring suffering and devastation to his “poor subjects.” Instead, he would rather leave revenge up to God. Monticelso mentions that he has a special book containing a list of every criminal in the city. He offers the book to Francisco so that they might find a criminal ally. Monticelso goes to fetch the “black book,” and in his absence, Francisco admits to himself that he will seek a slow, careful revenge against Bracciano.

Monticelso shows off his black book of criminals. He lists the names and crimes of those in the book, then leaves it with Francisco. Privately, Francisco wonders whether Monticelso uses the book for his own nefarious purposes. He then examines the book to find a murderer, keeping an image of Isabella in his mind to help him focus. Isabella’s ghost suddenly appears before Francisco, and he believes that his imagination is overly active due to his emotional turmoil. He asks the ghost a series of questions but then abandons the interview, causing the ghost to leave.