For four weeks, Lockwood has been ill, and Heathcliff has sent him grouse to eat. Nelly continues the story while supervising Lockwood’s medication regimen.

Six months into the marriage between Catherine and Edgar, all is well, until Heathcliff returns to Wuthering Heights unexpectedly. He is a changed man; “[h]e had grown a tall, athletic, well-formed man; beside whom, [Edgar Linton] seemed quite slender and youth-like” (69). Soon, Edgar feels jealous of Catherine’s enthusiasm over Heathcliff’s return. Catherine later reports to Nelly that when she praised Heathcliff to Edgar, “he, either for a headache or a pang of envy, began to cry” (70). Heathcliff has explained his reason for returning to Wuthering Heights to Catherine, who tells Nelly that Heathcliff has returned because he wants to live near the Grange and feels an attachment to Wuthering Heights.

Heathcliff takes advantage of his proximity to Thrushcross Grange by coming to visit often, and Isabella Linton falls swiftly and intensely in love with him. Catherine in turn mocks Isabella for her desire for Heathcliff, pointing out that Isabella’s inheritance is her most appealing quality to a man like Heathcliff. A confrontation between Isabella, Catherine, and Heathcliff leads him to wonder why Catherine has been teasing Isabella. She reveals Isabella’s affection for Heathcliff, and he agrees to set the issue aside.

Nelly feels chronic anxiety about the goings-on at Wuthering Heights, describing a visit she made to see Hareton. Hareton curses at her, having learned some bad habits from the man he calls “[d]evil daddy.” When Heathcliff appears, Nelly runs away.

The next time Heathcliff comes to Thrushcross Grange, Nelly observes him secretly interacting with Isabella: “supposing himself unseen, the scoundrel had the impudence to embrace her” (80). Nelly quickly tells Catherine what she has seen, and Catherine shouts to Heathcliff that he must leave Isabella alone, which angers him into retorting that she has no right to be jealous. Catherine and Heathcliff argue bitterly until he seems cowed by her tirade. When Edgar appears, Catherine provokes him as well, humiliating him. Later, Edgar confronts Catherine and insists that she choose between him and Heathcliff, which causes Catherine to hit her head repeatedly against a piece of furniture. The next morning, Catherine refuses to come downstairs, and Edgar and Isabella discuss Heathcliff; Edgar is clear about his feelings and warns Isabella that she will forfeit her status as his sister if she encourages Heathcliff.

Isabella remains heartsick and miserable, while Catherine refuses to eat meals with Edgar. Nelly brings Catherine tea and toast, only to listen to Catherine raving about her impending death; she mumbles at one point, “No, I’ll not die—he’d be glad—he does not love me at all—he would never miss me!” (87). In her delirium, Catherine misunderstands Nelly, who responds, thinking that Catherine is talking about Edgar. Catherine sees a vision of a face in the mirror and reports having nightmares, maintaining that “the whole last seven years of [her] life grew a blank” (91). As her fever intensifies, Catherine begs to open a window and be outdoors; eventually, she believes she sees a light in her old bedroom across the moors at Wuthering Heights and interprets it as a summons from Heathcliff. 

Edgar finally comes to see Catherine, and he is astonished to realize how ill she is. Nelly goes for a doctor, explaining to him that Catherine’s illness seems caused by intense emotion. The doctor reports having seen Isabella Linton with Heathcliff the night before, urging Nelly to tell Mr. Linton to be on guard. The doctor advises Edgar to keep Catherine calm, a difficult thing to accomplish once one of the servants announces that Isabella has run away with Heathcliff.

Under Edgar’s tender care, Catherine recovers from her delirium and fever just in time for the spring snow melt, but she still talks of her death nearing. Nelly believes her gloom stems from having spent so long indoors and in bed. Catherine is pregnant, which lifts Edgar’s spirits.

Edgar receives a note from Isabella announcing her marriage to Heathcliff. In a letter to Nelly, Isabella wonders if “Mr. Heathcliff [is] a man? If so, is he mad? And if not, is he a devil?” (99). She goes on in her letter to describe horrible conditions at Wuthering Heights, where Joseph and Hareton live in filth. Isabella describes a disturbing encounter with Hindley, who is now in debt to Heathcliff and threatening to kill him: “I will have it back: and I’ll have his gold too: and then his blood: and hell shall have his soul!” (103). Isabella closes the letter to Nelly with a mention of Catherine’s illness. Heathcliff blames Edgar for causing it, and he desires to punish Isabella as “Edgar’s proxy.” With regret and an exclamation of hatred against her husband, Isabella begs Nelly not to tell anyone at the Grange of her distress.