Catherine and Heathcliff grew up together and enjoyed each other’s company. They grew closer and closer as they grew, but when Catherine is bitten by the Linton’s guard dog and must recuperate at the Grange, she changes. At the Grange, Mrs. Linton decides to take Catherine on as a project, transforming her from a somewhat wild and unruly girl into a refined lady. She teachers her manners and social graces. At Christmas, Catherine returns to Wuthering Heights a changed young lady. She is wearing a frilly dress and Hindley only lets Heathcliff greet her as one of the servants, not as a former close friend. When Catherine sees Heathcliff after so long, she immediately notices that compared to the Lintons, Heathcliff is dirty. Heathcliff’s feelings are hurt and he storms away. Catherine has changed, but not totally. When the Lintons come for dinner the next day, they insist that Heathcliff be kept away. Hindley decides to lock Heathcliff in the attic but before doing so, he makes a nasty comment about Heathcliff’s hair and Heathcliff throws food at Hindley. Catherine then feels really bad about Hindley’s cruel treatment of Heathcliff and she goes to see him in the attic. Later, Heathcliff reacts with anger, telling Nellie that he will get even with Hindley some day. Oh boy, and does he!
After her time at the Grange, however, Catherine realizes that though she loves Heathcliff, she can never marry him. She realizes the difference in their social status. Later, she foolishly tells Nellie that she is going to marry Edgar Linton so that she can help Healthcliff. This is her naive way of trying to reconcile her love for Heathcliff with her understanding of their social differences. This is what also what sends Heathcliff over the edge.