At the theater, Dorian is surprised to find it crowded with people. He takes Lord Henry and Basil Hallward to his usual box and they discuss the crowd below. He tells them that Sibyl's art is so fine that she spiritualizes the common people, transforming their ugliness into beauty. Basil tells him he now agrees that the marriage will be a good thing for him.
When Sibyl appears on the stage, both men are entranced by her beauty, but when she starts to act, they are embarrassed for Dorian. Dorian doesn't speak, but he is horribly disappointed. Sibyl's acting is horribly wooden. The people below hiss and catcall to the stage making fun of her poor acting. After the second act, Lord Henry and Basil Hallward leave. Dorian tells them he will stay out the performance. He hides his face in anguish.
When the play is over, he goes to the green room to find Sibyl. She's waiting for him. She looks radiantly happy. She tells him she acted so badly because she loves him. She says that before she loved him, the stage was real and alive for her. she never noticed the tawdriness of the stage set or the ugliness of her fellow actors. She had put everything into it because it was all of her life. When she realized tonight that she was acting horribly, she was struck by the realization that it was because she had found a new reality.
When she finishes, Dorian tells her she disappointed him and embarrassed him horribly. He says she killed his love. Sibyl is shocked and horrified by his words. She begs him to take them back, but he goes on. he tells her he loved her for her art and now she has nothing of her art and so he doesn't love her any more. Now she is nothing but "a third-rate actress with a pretty face." Sibyl throws herself at his feet begging him to be kind to her, but he walks away scornfully, thinking how ridiculous she looks.
He walks through the poverty-stricken streets of London for a long time. Then he gets back to his room, recently redecorated since he learned to appreciate luxury from Lord Henry. He is undressing when he happens to glance at the portrait. He is taken aback to notice a change in it. Lines around the mouth have appeared. The face has a cruel expression. He turns on the lights and looks at it more carefully, but nothing changes the look of cruelty on the face. He remembers what he said in Basil's studio the day he saw it for the first time. He had wished to change places with it, staying young forever while it aged with time and experience. He knows that the sin he committed against Sibyl that evening had caused him to age. He realizes that the portrait will always be an emblem of his conscience from now on. He dresses quickly and hurries toward Sibyl's house. As he hurries to her, a faint feeling of his love for her returns to him.
The climax of the novel occurs in this chapter. Dorian takes his friends to see Sibyl's fine acting and is embarrassed by her dreadful acting. Even when she tells him she has lost her talent for acting because she loves him and thinks only of him, he doesn't soften toward her. He lets her sob and he leaves her coldly. The consequences of this sin of the heart is that Dorian Gray ages. However, it is not he that ages, but his portrait. Here, Oscar Wilde plays with the notion that art imitates life. When Dorian first saw his portrait, he wished for its timelessness. He wished he could change places with art, living the timelessness of art, and letting the portrait age and wither. In this climax chapter, that reversal seems to happen. Whether the reader is supposed to think of this as Dorian's guilty conscience projected onto the portrait or a depiction of magic is unclear at this point. The reader has to wait to find out if any other character besides Dorian will see the change in the portrait.