Some time has passed ad Isabel is now married. Shortly after her return to Florence, Isabel receives a visit from Caspar Goodwood, who is still in love with her and feeling anxious and uneasy. He tells her he would rather believe she were dead rather than married to someone else. It is at this point in the story that we learn Isabel has decided to marry Gilbert Osmond, but has only confided this to Caspar and Madame Merle, keeping it a secret from everyone else.

Caspar immediately set off for Italy after finding out about Isabel's marriage. He is upset and worried about Isabel's decision to marry Osmond, and his primary objective was to see her once more before they parted ways. Caspar is unable to understand why Isabel had chosen Osmond, and Isabel didn't attempt to explain or clarify her decision. She simply mentioned that she had initially planned to remain single, but changed her mind. Caspar departs feeling angry and wounded, while Isabel starts to cry as he leaves.

Isabel tells Mrs. Touchett that she plans to marry after Caspar leaves. Mrs. Touchett is very unhappy with her niece's decision and warns her that Madame Merle had arranged the marriage. Although her aunt cautions her that Madame Merle might be deceitful, Isabel finds it hard to believe.

Mrs. Touchett, despite her reservations, consents to allowing Isabel to exercise her own judgment. Ralph, who appears to be unwell and exhausted upon his return from Corfu, is distressed and ashamed to learn about the decision. He takes accountability for assuming that Isabel would eventually lose interest in Osmond. Meanwhile, Isabel spends her days with her betrothed, accompanying him on strolls through the sprawling Cascine park in Florence.

One morning, Isabel finds Ralph sitting in the garden of the Touchett estate, lost in thought about his cousin's upcoming marriage to Osmond. Ralph admits to Isabel that he does not approve of the union and has a low opinion of Isabel's fiancé. Isabel becomes offended and defends Osmond, stating that she admires his simple lifestyle. Ralph argues that Osmond is a self-centered and narrow-minded person who takes himself too seriously. Ralph believes that Osmond is not deserving of his cousin and is merely an amateur. Suddenly, Ralph reveals his love for Isabel but acknowledges that he does not have any hope of receiving her love in return.

Isabel is upset that Ralph thinks so poorly of Osmond. However, Ralph refuses to change his opinion and warns Isabel that she is making a huge mistake. He criticizes himself, remembering that he provided his cousin with the money to make her own choices. Ralph believes that Isabel will face serious consequences if she chooses to marry Osmond. Isabel responds angrily, telling Ralph that she will never seek his help in the future.

Isabel is not deterred by her family's disapproval of her engagement, and spends her afternoons with Osmond in the park without hesitation. Osmond is thrilled to be engaged to Isabel and expresses his happiness, stating that he has never felt more content. He recognizes Isabel's charm and intelligence, and believes that they are well-suited for each other. Osmond acknowledges that the Touchetts do not approve of him, as they suspect he is only interested in Isabel's wealth. However, he assures Isabel that his affection for her is not motivated by her money, and is confident that they will enjoy a fulfilling life together.

Pansy is glad that her father is marrying Isabel, and she is excited to welcome her into the family. Despite being 16 years old, Osmond's daughter remains pure and kind. The Countess Gemini, Osmond's sister, is also happy about the news and believes that Isabel will be a valuable addition to their family. The Countess notes that the Osmonds were once a respectable family, but have since experienced a decline. She hopes that Isabel will be able to assist in restoring the family's reputation.