At another fancy evening ball at the Lintons, Isabella has invited Heathcliff as her guest, and it worries her brother Edgar:

Oh, it's just a young girl's fancy, but one has to be careful not to enflame it with too much opposition.

Cathy feels Heathcliff's dark eyes staring at her during a harpsichord concert, realizing that Heathcliff may find his revenge (or incite her jealousy) by romancing her sister-in-law. In the moonlight while getting a "breath of fresh air," Heathcliff finds a moment to speak to Cathy. He expresses his undying love to her once again:

Cathy: You're very grand Heathcliff, so handsome. Looking at you tonight, I could not help but remember how things used to be.
Heathcliff: They used to be better.
Cathy: Don't pretend life hasn't improved for you.
Heathcliff: Life has ended for me. (A long pause) How can you stand here beside me and pretend not to remember? Not to know that my heart is breaking for you. That your face is the wonderful light burning in all this darkness.
Cathy: Heathcliff no, I forbid it.
Heathcliff: Do you forbid what your heart is saying to me now?
Cathy: It's saying nothing.
Heathcliff: It 'tis. I can hear the love of the music. Oh Cathy, Cathy.
Cathy: I'm not the Cathy that was. Can you understand that? I'm somebody else. I'm another man's wife and he loves me. And I love him.
Heathcliff: If he loved you with all the power of his soul for the whole lifetime, he couldn't love you as much as I do in a single day. Not he, not the world. Not even you Cathy can come between us.
Cathy: Heathcliff, you must go away. You must leave this house and never come back to it. I never want to see your face again or listen to your voice again as long as I live.
Heathcliff: You lie. I did come here tonight because you willed it. You willed me here to cross the sea.

After the party, Cathy demands to speak to Isabella about Heathcliff, thinking she behaved "disgracefully" and made a spectacle of herself by throwing herself at him. And then she tries to warn her sister-in-law of his moodiness and vengeful motives, but Isabella accuses Cathy of simply being jealous and wanting Heathcliff's attention all for herself:

Cathy: You fool, you vain little fool. I'll not be silent any longer. I'm going to tell the truth. You're old enough to hear it and you're strong enough...Don't you see what he's been doing? He's been using you to be near me. To smile at me behind your back. To try to rouse something in my heart instead. I'll not have it any longer. I'll not allow you to help him any longer.
Isabella: You were vain and insufferable. Heathcliff's in love with me.
Cathy: It's a lie.
Isabella: It's not a lie. He's told me so. He's kissed me.
Cathy: He's...
Isabella: He's kissed me. He's held me in his arms. He's told me that he loves me.
Cathy: I'm going to your brother.
Isabella: Go to him. He's asked me to marry him. Tell Edgar that, that we're going to be married, that Heathcliff's going to be my husband.
Cathy: Isabella, you can't. Heathcliff's not a man, but something dark and horrible to live with.
Isabella: Do you imagine, Catherine, that I don't know why you're acting so? Because you love him. (Cathy slaps Isabella) Yes, you love him and you're mad with pain and jealousy with the thought of my marrying him. (Cathy slaps Isabella again) Because you want him to pine for you and dream of you, die for you while you live in comfort and security as Mrs. Linton. You don't want him to be happy! You want to make him suffer! You want to destroy him! But I want to make him happy. I will, I will!

To plead with Heathcliff to not carry out his plan to lovelessly marry Isabella (and thereby abandon her), Cathy goes to Heathcliff at Wuthering Heights, but he remains implacable:

Cathy: Oh Heathcliff, you must not do this...she hasn't harmed you.
Heathcliff: You have.
Cathy: Then punish me.
Heathcliff: I'm going to. When I take her in my arms, when I kiss her, when I promise her life and happiness.
Cathy: Oh Heathcliff, if there's anything human left in you, don't do this! Don't make me a partner to such a crime. It's stupid, it's mad!
Heathcliff: If you ever looked at me once with what I know is in you, I would be your slave. Cathy, if your heart were only stronger than your dull fear of God and the world, I would live silently contented in your shadow. But no, you must destroy us both with that weakness you call virtue. You must keep me tormented with that cruelty you think so pious. You've been smug and pleased with my vile love of you, haven't you? Haven't you? (Cathy turns to leave) Well, after this, you can think of me as something else than Cathy's foolish and despairing lover. You can think of me as Isabella's husband. (Cathy turns back) And be glad for my happiness as I was for yours.

Emotionally tormented by Heathcliff's spiteful decision to marry her sister-in-law and thereby crush their former love, Cathy pleads with Edgar to stop the marriage. She causes him to doubt Cathy's love for him within their own marriage.

And so, Heathcliff and Isabella were married. And many months later at Wuthering Heights...

Indeed, Heathcliff finds his revenge by marrying and then neglecting Edgar's sister Isabella. His post-marital cold indifference and abominable treatment forces her to wither, and she realizes too late that Cathy was right. Dr. Kenneth (Donald Crisp), the family doctor, advises that Isabella (considered "disowned") return to the Grange, because Cathy is "gravely ill." In fact, Cathy is dying of a broken heart and lacking of the will to live:

Fever, inflammation of the lungs, something beyond that. I don't know. I'd call it the will to die.

Isabella speculates that Cathy's death may help her own marriage and turn Heathcliff's love toward her at last:

If Cathy died, I might begin to live.

Almost pleased that Cathy is near death, Isabella encourages her unloving husband to change and direct his pain and revenge into passion toward her:

Heathcliff: Why isn't there the smell of heather in your hair?
Isabella: Oh Heathcliff, why won't you let me come near you? You're not black and horrible as they all think. You're full of pain. I can make you happy. Let me try. You won't regret it. I'll be your slave. I can bring life back to you, new and fresh.
Heathcliff: Why are your eyes always empty? Like Linton's eyes.
Isabella: They're not empty, if you'd only look deeper. Look at me. I'm pretty. I'm a woman and I love you. You're all of life to me. Let me be a single breath of it for you. Heathcliff, let your heart look at me just once!
Heathcliff: Almighty God, give me life. What is it but hunger and pain?

When Heathcliff learns from Ellen that Cathy is sick and dying of an incurable disease (and that Edgar wants Isabella to return home to assist), Heathcliff rushes on horseback to the Grange. On her deathbed, Cathy deliriously asks Edgar to get her some heather from her make-believe, imaginary castle on Peniston Crag among the heather:

Cathy: My heather. There's a beautiful patch by the castle. I want some from there...the castle on the moors, Edgar. Go there please.
Edgar: There's no castle on the moors, darling.
Cathy: There is. There is. It's on the hill beyond Wuthering Heights.
Edgar: You mean Peniston Crag.
Cathy (smiling): Yes. Yes. I was a queen there once. Go there, Edgar. Get me some heather please.

After Edgar leaves, Heathcliff runs up and sneaks into Cathy's room, and together they share one of the most memorable, luminous deathbed scenes ever filmed. There, they pledge their enduring, undying love and become reconciled after so many years of mutual unhappiness and bitterness:

Cathy: Heathcliff. Come here.
Heathcliff: Cathy...
Cathy: I was dreaming that I wake up before I die, that you might come and scowl at me once more.
Heathcliff: Cathy...
Cathy: Oh, Heathcliff. Oh how strong you look. How many years do you mean to live after I'm gone? (They passionately hug and kiss each other, finally revealing their truest emotions to each other) Don't, don't let me go. If I could only hold you until we were both dead. Will you forget me when I'm in the earth?
Heathcliff: I could as soon forget you with my own life, Cathy, if you die.
Cathy: Boy, Heathcliff. Come. Let me feel how strong you are.
Heathcliff: Strong enough to bring us both back to life, Cathy, if you want to live.
Cathy: No, Heathcliff, I want to die.
Heathcliff: Oh Cathy, why did you kill yourself?
Cathy: Hold me. Just hold me.
Heathcliff: Oh, and love comfort you. My tears don't love you, Cathy. They blight and curse and damn you!
Cathy: Heathcliff, don't break my heart.
Heathcliff: Oh Cathy, I never broke your heart. You broke it! Cathy! Cathy! You loved me! What right to throw love away for the poor fancy thing you felt for him, for a handful of worthiness. Misery and death and all the evils that God and man could have ever done would never have parted us. You'd be better alone. You wandered off like a wanton, greedy child to break your heart and mine.
Cathy: Heathcliff, forgive me. We've so little time.

When Ellen warns that Mr. Linton is returning, Heathcliff vows to stay with Cathy as her strength ebbs. He hears her claim that he was always the only man she ever loved:

Heathcliff: I won't go, Cathy. I'm here. I'll never leave you again.
Cathy: I told you, Ellen. When you went away that night in the rain, I told you I belonged to him, that he was my life, my being.
Ellen: Don't listen to her ravings.
Cathy: It's true. It's true. I'm yours, Heathcliff. I've never been anyone else's.
Ellen: She doesn't know what she's saying. You can still get out. Go before they get here.
Cathy: Take me to the window. Let me look at the moors with you once more. My darling, once more.

Heathcliff carries her in his arms to the window, where they look out on the moors and the Crag where they played together as children. Before slumping into his arms after breathing her last breath, they make a pact to be together for eternity. She promises to wait for him there in death until they are reunited again one day:

Heathcliff, can you see the Crag over there where our castle is? I'll wait for you 'til you come.

When Dr. Kenneth enters the bedroom with Edgar, Heathcliff tells them: "Leave her alone - she's mine." While they pray for Cathy's soul, a distraught Heathcliff gives an impassioned plea to his deceased beloved to haunt him for the rest of his days. He wishes that he won't have to suffer a long separation:

Ellen: Oh my wild heart! Miss Cathy. She's gone! She's gone!
Dr. Kenneth: You've done your last black deed, Heathcliff. Leave this house.
Edgar: She's at peace now, in Heaven beyond us.
Heathcliff: What do they know of Heaven or Hell, Cathy, who know nothing of life? Oh, they're praying for you, Cathy. I'll pray one prayer with them - I repeat 'til my tongue stiffens - Catherine Earnshaw, may you not rest so long as I live on! I killed you. Haunt me, then! Haunt your murderer! I know that ghosts have wandered on the Earth. Be with me always. Take any form, drive me mad, only do not leave me in this dark alone where I cannot find you. I cannot live without my life! I cannot die without my soul!

With Cathy's death scene ended, the film returns to the end of Ellen's narration, told to Mr. Lockwood in front of the fireplace at Wuthering Heights.

Ellen: I can still see and hear that wild hour, with poor Heathcliff trying to tear away the veil between death and life, crying out to Cathy's soul to haunt him and torment him 'til he died.
Lockwood: You say that was Cathy's ghost I heard at the window?
Ellen: Not a ghost, but Cathy's love, stronger than time itself, still sobbing for its unlived days and uneaten bread.

Dr. Kenneth enters the room, claiming to have seen Heathcliff walking the moors with a woman. After desperately searching for Cathy's ghost in the snowy cold storm, Heathcliff freezes to death. His soul joins his love in death at their favorite place forevermore:

Dr. Kenneth: I tell you, I saw them both. He had his arm about her. So I climbed up after them. And I found him, only him, alone, with only his footprints in the snow.
Ellen: Under a high rock on a ledge near Peniston Crag.
Dr. Kenneth: Yes.
Lockwood: Was he dead?
Ellen: No not dead, Dr. Kenneth. Not alone. He's with her. They've only just begun to live. Goodbye Heathcliff. Goodbye my wild sweet Cathy.

In the final memorable image, the young, ghostly spirits of Cathy and Heathcliff are re-united for eternity (super-imposed as they walk over the snow) in death on Peniston Crag, where they had spent many happy hours together in their childhood walking joyously across the heath.

[Note: The final scene with its famous closing shot was actually filmed after the original cast was released. Producer Samuel Goldwyn insisted on a different ending than the tragic one Wyler had made, more upbeat than a final shot of Heathcliff's body. So he hired an assistant director to reshoot a new ending with stand-in doubles for the two main stars.]