The sweet, wholesome Sibyl discusses her engagement with her family. Because her mother is indebted to the theatre manager, Mr. Isaacs, for fifty pounds, she is against the marriage unless Dorian is wealthy; they do not know that he is. Sibyl's angry brother, James, is leaving for Australia, but he vows to kill Dorian if he wrongs his sister in any way. James also confronts his mother about gossip he has heard — that his mother and deceased father never married, which Mrs. Vane admits is true.
Dorian attends a performance of Sibyl's with Lord Henry and Basil, but the performance is terrible. Sibyl tells Dorian she can no longer act, because he has shown her a beautiful reality. Dorian is disgusted by her poor acting, because her performances were what drew him to her; he dismisses her and returns home. To his surprise, the portrait shows marks of cruelty around the mouth, lines that do not show on Dorian's face. He begins to suspect that his wish is coming true, so he vows to be good so that both he and the portrait can remain young. He, therefore, intends to apologize to Sibyl the next day and makes to marry her after all.
However, he is too late: Sibyl commits suicide at the theatre that night. Dorian first feels responsibility for her death, but then views it both as wonderful entertainment and a selfish act on her part. Lord Henry tries to keep Dorian's name out of the scandal. Dorian and Lord Henry spend the evening at the opera. The next morning, Basil arrives and expresses concern for Dorian, given the events of the previous day. Dorian, however, is completely unconcerned about Sibyl or her family; he wants to talk only of happy subjects. The next day, he covers his portrait and moves it to the attic, to which Dorian has the only key. He then settles in to read a yellow book sent by Lord Henry; the book becomes Dorian's blueprint for life.
