The plot of Emily Bronte's Wuthering Heights, although it involves a number of complex relationships, largely revolves around Heathcliff's pursuit of revenge. We see how revengeful can a person be for his unrequited love through Heathcliff’s character. Heathcliff's revenge is apparent in how he treats the Earnshaws, degrading Hindley and Hareton just as Hindley did him. This is also shown in his actions against the Lintons. Heatcliff’s great love for Catherine lies behind all his brutal actions.
Heathcliff deliberately ruins Hindley. Heathcliff hates the Lintons because Cathy married Edgar. He treat brutally with Isabella, Edgar Linton’s sister, Heathcliff uses his treachery to steal away the Linton fortune and to degrade their offspring. Heathcliff's revenge is shown in how he treats Cathy herself. He loves her so much he hates her. He feels that Cathy betrayed her heart and married Edgar. He pursues his revenge through Hareton, the son of Hindley and Catherine the daughter of Edgar Linton. His treatment of his own sick son Linton is no better.
Hindley reduced Heathcliff to such a status that it would ruin Cathy to marry him. When Heathcliff returns to Wuthering Heights after several years, his frustration leads him to exact revenge on Hindley Earnshaw. He sets out deliberately to ruin Hindley, lending him money to gamble and drink and then getting him to mortgage the Heights to him so that he eventually becomes the master of the Heights. He returns the favour to Hindley, reducing him and his son Hareton to servant class. This is apparent when Heathcliff is talking to Nellie about his joy in degrading Hareton, he says, I've pleasure in him!..He has satisfied my expectations…”
Cathy married Edgar Linton for his status and wealth, betraying her love for Heathcliff. So, Heathcliff takes revenge by his vengeful actions against the Lintons. Heathcliff seeks to destroy the entire Linton family. Heathcliff achieves this by marrying Isabella Linton. Isabella believes that Heathcliff is a kind decent man; however, soon after she marries him, he becomes abusive. This is shown in a letter from Isabella to Nellie in which she says, ..he is ingenious and unresting in seeking to gain my abhorrence!..I assure you, a tiger, or a venomous serpent could not rouse terror in me equal to that which he awakens.
His revenge is also shown when he talks to Cathy when she is sick. This is apparent when Heathcliff says, 'Why did you betray your own heart, Cathy? I have not one word of comfort - you deserve this. You have killed yourself..They'll blight you - they'll damn you. You loved me - then what right did you to leave me?..I have not broken your heart - you have broken it - and in breaking it, you have broken mine.' This quote shows Heathcliff's anger, and his blaming of Cathy. His acute revengeful mentality is exposed through such words. Heathcliff is so angry that he condemns her soul when she dies, hoping that she may never rest in peace, that her spirit will always wander the earth, anything just so long as she does not leave him again. This shows Heathcliff's love for Cathy; his love is strong enough to cause him to curse her soul rather than go without her.
His desire for revenge however doesn’t end with the death of Hindley or with Isabella’s escape from the Heights. He pursues his revenge through Hareton, the son of Hindley, and Catherine the daughter of Edgar Linon. He treats Hareton as he had been treated by Hindley. Hareton is deprived of education, fumed into a mere farm land and treated as a servant.
Heathcliff has imprisoned Catherine, the daughter of his beloved Cathy, till he can forcibly get Catherine married to Linton. Catherine is deliberately kept in the dark about Linton’s grave state of health. Heathcliff violently hits her when Catherine bites him in a bid to escape and he does not let her visit her dying father.
His treatment of his own sick son Linton is no better. He claims rights over his son Linton but has no love for the sickly boy. He terrorizes and mistreats even his own son because of his blood relation with Linton family. He forces him to woo Catherine, so that a marriage between them would make Heathcliff the master of Thrushcross Grange, after the death of his son. He is totally callous, unfeeling and cruel when he refuses to get a doctor for his dying son as he feels that his life is not worth a farthing. Even when Linton Heathcliff lets Catherine escape, he punishes the sick boy and makes sure Catherine is back at the Heights, immediately after the funeral of her father.
He is revengeful because of his unrequited love for Cathy. His revenge is shown through his actions towards the Earnshaws, a famliy that degraded him, the Lintons, the people he believes stole Cathy away from him, and Cathy herself, the woman he feels betrayed her heart and his love. He felt that he did not have Cathy's love, when all the time he truly owned her heart. Heathcliff did everything for his unrequited love.