That night, Hindley grabs Hareton from Nelly in a rage, but then accidentally drops the baby over the bannister. Luckily, Heathcliff is at the bottom of the steps to catch Hareton without harm.
This odd, almost grotesque scene adds to the Gothic menace of the novel.
Later, Catherine goes to Nelly in the kitchen. As Heathcliff listens, she tells Nelly that she has accepted Edgar's proposal of marriage, yet isn't sure she should have. Catherine describes a dream in which she was in heaven but didn't feel at home; when angels returned her to Wuthering Heights, she was relieved. She equates marrying Edgar to such a heaven.
The heaven of Catherine's dream is a pleasant, civilized place. But her dream implies that though she finds those things attractive, she'll never escape the wild, passionate part of her nature that is symbolized by Wuthering Heights—and which loves Heathcliff.
Yet she also says that she cannot marry Heathcliff because Hindley has so degraded Heathcliff that marrying him would be like degrading herself.
Hindley's revenge is a success: even Catherine is affected by Heathcliff's fall to a lower class.
Furious and ashamed, Heathcliff leaves, and therefore doesn't hear Catherine say that, though she must marry Edgar, she loves Heathcliff more than anything and that nothing could interfere in their relationship, not even marrying Edgar, because she and Heathcliff are, essentially, the same person.
Yet Catherine is at the same time so passionate about Heathcliff that she can't see how anything can come between them. She's wrong. She doesn't understand that nature (i.e. Heathcliff) won't be chained or denigrated.
That night, in a storm, Heathcliff runs away from Wuthering Heights. Catherine discovers his absence and, distraught, searches for him all night in the rain, catching a fever in the process.
Another storm, and more passionate plot points. Note that a fever is like a physical manifestation of wild passion.
The Lintons nurse Catherine through the fever at Thrushcross Grange, but Mr. and Mrs. Linton themselves come down with the sickness and die.
The civilized Linton's try to cure Catherine's fever (i.e. passion), but instead they are killed by it.
Three years later, Heathcliff has still not returned, and Edgar and Catherine get married. Nelly leaves Hareton with Hindley and Joseph at Wuthering Heights and moves to Thrushcross Grange.
The three year wait before Edgar and Catherine marry indicates Catherine's continued attachment to Heathcliff.