Whenever Father Ambrosio speaks in the church, all Madrid goes to hear him. He is the most learned, the most virtuous, and the most admired monk in the city. Such is his purity that he will tolerate no sin in others, and he berates the worshipers viciously. In the audience one day is a young woman named Antonia, who comes to Madrid with her mother to seek the financial aid of their relative, the Marquis Raymond de las Cisternas. At the church, Antonia meets Lorenzo de Medina, a wealthy young nobleman who, charmed by her sweetness, promises to petition Raymond in her behalf. Before he leaves the church, Lorenzo sees Raymond and learns that he is the man who supposedly spurned Lorenzo's sister Agnes and caused the heartbroken girl to enter the convent of St. Clare. Lorenzo challenges his former friend, but Raymond begs him to hear the story and then make his judgment.