For several days, Isabella mopes around, Catherine pouts in her room, and Edgar worries about his wife. Catherine believes she is dying and is infuriated when Nelly Dean tells her that Edgar has been reading contentedly in the library, in "philosophical resignation" (12.18). (Of course, Nelly is just trying to make Catherine mad – and it works!)
Catherine actually does get sick and, in a feverish delirium, she begins to name all of the bird feathers coming out of her pillow. She starts hallucinating, doesn't recognize her own reflection in the mirror, and tells Nelly that in her confused state she thought she was back home at Wuthering Heights. She starts to recall her childhood – the oak-paneled bed, the wild adventures on the moors, and her love of Heathcliff.
Now completely babbling and convinced she is at death's door, she raves, "I'll not lie [in the ground] by myself; they may bury me twelve feet deep, and throw the church down over me, but I won't rest until you are with me. I never will!" (12.52).
Edgar finally comes to see Catherine. Nelly wises up and goes to seek medical attention. In the garden, she finds Isabella's pet dog, Fanny, hanging by the neck, nearly dead. The sounds of galloping horses echoes in the distance.
Mr. Kenneth tells Nelly that he has heard on "good authority" that Isabella has run off with Heathcliff. Nelly is too scared to tell Edgar, but when he does find out, he seems resigned to her decision.