Cathy is not happy to have lost her new cousin and playmate so quickly.
The housekeeper from the Heights updates Nelly on how things are going between Linton and his father—as expected, not good. Linton is sick all of the time and is "selfish and disagreeable" (21.6).
On her sixteenth birthday, Cathy announces that she would like to spend the day on the moors. Of course, she begins to make her way toward Wuthering Heights, and she and Nelly run into Heathcliff, who invites them back to the house, insisting that Cathy come see Linton.
As he drags them back to the house, Heathcliff announces his plan to have the cousins (Cathy and Linton) get married, so that he can inherit the Grange when Edgar dies. It's all about property.
Cathy is thrilled at finding these relatives living so near to the Grange and chastises Nelly for not telling her about them. Heathcliff mentions Edgar's "prejudice" against him and complains to Nelly that his own son is a wimp.
Heathcliff explains to Nelly that he sympathizes with Hareton and yet has enjoyed mistreating him, degrading him, and turning him into an animal who scorns "book-larning"—all as revenge against his father, Hindley.
Heathcliff enjoys pitting Hareton against his son in an effort to make Linton seem more appealing to Cathy, simply because he has a glimmer of intelligence next to his oaf of a cousin.
Rather than keep the visit a secret, Cathy announces it to her father the next day. Edgar tells her the whole dark story: how Heathcliff ran away with Aunt Isabella and desires only revenge.
Cathy wants to begin writing letters to Linton. When Nelly refuses to help her, Cathy finds a milk-fetcher to be her delivery boy. She quickly accumulates a mass of letters, which she hides in a drawer. Nelly collects them all, and when she confronts Cathy about her disobedience, she finds out that Cathy is in love with Linton.
Nelly burns the letters and puts an end to the correspondence.