Nelly continues her story: the following summer, Frances gives birth to a son, Hareton Earnshaw. But Frances dies just a week later—childbirth had aggravated a case of consumption that she had long suffered from. Hindley is devastated. He hands the baby over to Nelly to care for. He turns to alcohol for comfort, and takes out his grief on the servants, Catherine, and, especially, Heathcliff. For his part, Heathcliff delights in Hindley's decline.
The "civilized" characters in the novel are often weak or sickly. Hindley's grief is excessive, which at the time was a trait associated with women. Meanwhile, Heathcliff's own desire for revenge has made him almost coldblooded—he feels no sympathy for Hindley's loss and actually delights in his pain.
Catherine remains in touch with the Lintons. When she's with them she acts like proper lady. But when with Heathcliff, she acts just as she used to.
Catherine now bridges the gap between civilization and nature...
One day when Hindley is out, Heathcliff doesn't go to the fields and instead plans to spend the day with Catherine. But Catherine admits that she's invited Edgar and Isabella to come visit. Heathcliff comments on how much time Catherine has been spending with the Lintons, she retorts that it's because he, Heathcliff, is dull and dumb. Edgar arrives just then, alone. Heathcliff storms out.
...but it isn't possible to span this gap for long without causing some sort of conflict. And Catherine chooses civilization and class over her natural connection to Heathcliff. Edgar's arrival without Isabella signals that there is a romance between him and Catherine.
Catherine then tells Nelly to leave the room, since she wants to be alone with Edgar. Nelly refuses—Hindley had told her to chaperone Catherine. Furious, Catherine slaps and pinches Nelly, and even shakes the crying Hareton. Edgar tries to step in, but Catherine boxes his ears. Shocked and defeated by Catherine's wild behavior, Edgar rushes from the house. But as he leaves he catches a glimpse of Catherine, and captured by her beauty, he returns.
Yet it becomes clear right away that the civilized Edgar can't possibly stand up to the Catherine's fierce, natural passions. In fact, when they are together it is Catherine who takes on the stereotypical male role of power, and Edgar who accepts the more stereotypically passive role of a woman.
Nelly leaves Catherine and Edgar alone. When she does later enter to warn them that Hindley has come home, drunk and angry as usual, she has the sense that they have professed their love for each other.
It is interesting that Edgar must make his declarations of love quietly, in private. It's hard to imagine Heathcliff doing the same.