As her brothers and sisters grow up, Lucrezia witnesses the plans for the dynastic marriage of her sister Maria to the Duke of Ferrara. However, a succession of rainy days leads to Maria’s catching a fatal lung disease.

Only a month after Maria’s burial, Lucrezia eavesdrops on a conversation between her father and his adviser, Vitelli, in which Vitelli confesses that Ferrara would be open to marrying Lucrezia, whom he has held in high esteem since meeting her as a child. While Cosimo initially protests that Lucrezia is too young, he allows Vitelli to inquire as to whether she has had her period yet and, thus, reached womanhood.

A traumatized Lucrezia returns to the nursery shaken, and Sofia demands to know what is troubling her. When Sofia hears the news, she states that while she cannot prevent the marriage, she will be able to postpone it. This will involve some dissimulation in pretending that 12-year-old Lucrezia has not yet started her period. Thus, when Vitelli awkwardly inquires into this subject, Sofia insists that Lucrezia has not. Lucrezia remains still and unreactive during this conversation so as not to spoil their plan. It will be up to Sofia to tell Vitelli when the girl beings menstruating.