Catherine receives a letter from Isabella the next morning. Isabella apologizes for failing to write Catherine. She writes that she is uneasy about James, with whom she has had a misunderstanding. She hopes that Catherine will convince James that he is the only man she ever loved. She mentions the new style of hats, and then says that she will not speak ill of the Tilneys, but that young men never know their own minds. She says that Captain Tilney, her least favorite young man, has left Bath and she is glad of it. He spent the last two days there with another girl. She fears that James had a cold and was depressed when they parted, and that he may have misinterpreted her conduct. Catherine understands immediately that this letter is an attempt to manipulate her, and she swears that she will never mention Isabella’s name to James again.
Catherine is now better equipped to judge and understand Isabella’s hypocrisy. She has heard from James that Isabella planned to leave him for Frederick, and from the Tilneys has been helped to see that Isabella wants to marry for money. She sees that Isabella’s lack of loyalty to James has been paid back by Frederick with a lack of loyalty to her. Isabella’s hypocrisy may also stand out more boldly when written down, so Catherine can see it more clearly. It takes very little reading between the lines to see that Isabella has been dumped by Frederick and wants to make up with James.
Catherine reads the letter aloud to Henry and Eleanor and denounces Isabella, saying she wishes she had never known her. She congratulates them that their brother has escaped Isabella’s clutches, but says she still does not understand Captain Tilney’s behavior. Why, she asks, did he get between Isabella and James if he never intended to marry her? Henry says he does not wish to defend his brother, who has his vanities, but has managed to protect himself from being hurt by them, as Isabella has failed to do. Catherine asks if Frederick never cared about Isabella, and Henry says he thinks he never did. Catherine says she does not like Frederick for what he did, because he could have made Isabella fall in love with him. Henry says she would have had to be a different person then, and if she were a different person, she would have been treated differently.
Catherine still has trouble imagining that someone could be so casually insensitive to others’ feelings as to lead a woman on the way that Frederick did Isabella, especially someone related to the admirable and honorable Henry. Henry suggests that Isabella’s insincere professions of love for James and disloyalty to him once she saw the potential to marry someone richer make her the kind of person who deserves this kind of treatment. Although Catherine doesn’t notice this comment, it suggests that Henry believes that like should be repaid with like, and that the loyal and sincere Catherine should expect loyalty and sincerity from him. At the same time Henry is being somewhat harsh here, considering the systemic sexism of his society—for Isabella this scandal will mean ruin, but for Frederick it is presumably just a brief dalliance that will be overlooked by society.
Catherine thinks it is right of Henry to stand up for Frederick, and Henry says that if she were to truly stand up for her brother, she would be glad that he found out about Isabella’s character before it was too late, but her “mind is warped by an innate principle of general integrity.” Catherine is charmed by Henry, decides to attempt to forgive Frederick for his brother’s sake, and resolves to forget about Isabella entirely.
Henry is gently trying to help Catherine grow out of her innocent incomprehension of the bad and insincere behavior of others to become a better judge of character. He thinks her loyalty to her brother should make her grateful that James found out in time that he was engaged to an insincere and disloyal woman in Isabella.