Hindley comes home in a drunk and violent state. When Nelly Dean tries to shield Hareton from his father's wrath, Hindley puts a knife in her mouth.
Hindley drops Hareton from the top of the stairs and Heathcliff catches him. Though he desires nothing more than to ruin Hindley, Heathcliff rescues the child on instinct. Giving no thanks, Hindley proceeds to drink, seethe, and rave.
Nelly Dean consoles baby Hareton in the kitchen. Catherine comes in for a little one-on-one with her. Neither realizes that Heathcliff can hear the whole conversation.
It turns out Edgar has asked Catherine to marry him. She cites the various reasons she loves him, but admits that it doesn't feel right. She and Heathcliff are made of the same stuff, but Hindley has brought Heathcliff so low that, even though she loves him, it would degrade her to marry Heathcliff.
Nelly realizes that Heathcliff has overheard the confession up to this point. He has now departed.
Catherine foolishly believes she will be able to maintain her friendship with Heathcliff after she marries Edgar.
She makes the vital distinction between her love for the two men: "My love for Linton is like the foliage in the woods. Time will change it. […] My love for Heathcliff resembles the eternal rocks beneath […]. Nelly, I am Heathcliff—he's always, always in my mind […]" (9.101).
Things might have gone a little differently if Heathcliff had heard that last bit, no?
Nelly tells Catherine that Heathcliff heard part of her confession and that he has left Wuthering Heights. Catherine becomes hysterical.
Now Catherine is sick, and Mr. Kenneth, the village doctor, "pronounced her dangerously ill" (9.147). Catherine goes to convalesce at Thrushcross Grange. While she is there, Mr. and Mrs. Linton (parents of Edgar and Isabella) both die from Catherine's fever.
Three years go by and Catherine and Edgar marry. Nelly moves with the couple down to Thrushcross Grange, where they will live with Isabella Linton.
Hindley, Hareton, and Joseph stay at Wuthering Heights.