At Thrushcross Grange, Isabella mourns silently, Edgar withdraws among unopened books, and Catherine remains locked in her room without food. Nelly assumes Catherine is exaggerating until Catherine finally asks for water and gruel, saying she believes she is dying. Catherine eats eagerly but continues to rage that Edgar does not care, imagining his indifference and threatening either to starve or recover and leave the country.

Catherine’s condition worsens into feverish delirium. She tears open a pillow, fixates on feathers and memories of the moors with Heathcliff, mistakes Nelly for an old witchlike figure, and becomes terrified of her own reflection in the mirror. Catherine then recalls waking after her quarrel with Edgar and imagining herself back at Wuthering Heights as a child, before the last seven years of marriage and separation from Heathcliff had happened.

Longing for the freedom of the Heights, Catherine opens the window despite the winter cold and imagines seeing lights at Wuthering Heights. In her delirium, Catherine speaks as if to Heathcliff, declaring that she will not rest in the grave unless Heathcliff is with her. Edgar enters, horrified by Catherine’s appearance, and blames Nelly for not telling him how ill Catherine has become. Catherine rejects Edgar’s comfort, warns him not to mention Heathcliff’s name, and accuses Nelly of betrayal when the quarrel turns to Heathcliff’s visits and Isabella.

Nelly leaves to fetch Mr. Kenneth and, outside, finds Isabella’s dog Fanny nearly hanged from a bridle hook. On the way back with the doctor, Kenneth tells Nelly that Isabella and Heathcliff had been seen together the previous night and that Heathcliff urged Isabella to flee with him. Nelly discovers Isabella’s room empty and realizes Isabella has eloped, but keeps silent temporarily because Edgar is overwhelmed by Catherine’s crisis.

Mr. Kenneth examines Catherine and tells Edgar that Catherine may recover if kept perfectly calm, though he privately warns Nelly that Catherine risks permanent mental disturbance. In the morning, Mary blurts out that Isabella has run away with Heathcliff, confirming a report from Gimmerton that the pair stopped near midnight to have a horse shod. Edgar accepts that Isabella left willingly and refuses pursuit, declaring that Isabella has disowned him and is now his sister only in name.