As Mr. Earnshaw gets older (and sick), he becomes more and more protective of Heathcliff. His preferential treatment doesn't help the young boy one bit.
Thankfully, Hindley goes off to college.
Meanwhile, Catherine is growing up into a little troublemaker herself, but she's still sweet and pretty, and an Earnshaw, so she gets away with it. Her biggest problem, according to Mrs. Dean, is that she is overly fond of Heathcliff. She is with him all the time.
Inevitably, Mr. Earnshaw dies, and now all Heathcliff has is Catherine. With no one else in the house liking him, trouble looms.