During the walk home from Henry's, Dorian enjoys the warm evening. He is annoyed when several people mutter his name in astonishment as he passes, an occurence that used to please him, but he cheers himself by thinking of the beautiful and innocent Hetty, and his recent "good action." She had been hopelessly naive, but this was her charm, "she had everything that he had lost." He arrives at home and looks at his face in a mirror given to him by Henry long ago, but is so overcome with loathing that he shatters the mirror on the floor. He tries to focus on the future, to block out people like James Vane, now "hidden in a nameless grave," Alan Campbell, who shot himself without betraying Dorian's secret, or Basil Hallward, who Dorian "murdered in the madness of a moment." He attempts to assuage his guilt by blaming all of his troubles on Basil's portrait, and by contemplating the new life he has begun. He thinks of Hetty, the preservation of whose innocence he holds as proof of his newfound goodness, and wonders whether his good deed has caused his portrait to change for the better. He climbs to the attic, locks the door behind him, and throws the curtain from the picture.
A horrified gasp escapes his lips when he sees "no change, save that in the eyes there was a look of cunning, and in the mouth the curved wrinkle of the hypocrite." Dorian realizes that his kindness towards Hetty was either an act of vanity, driven by his desire to improve the appearance of his soul, or simply a different sort of selfishness, driven by "the desire for a new sensation." Desperate to escape his past crimes, Dorian sees the painting as the one piece of evidence revealing his guilt: "It had been like a conscience to him...He would destroy it." The knife on the table, he notices, is still stained with Basil's blood. He takes it, cleans it several times, and stabs the picture.
Dorian's servants are awoken by a dreadful shriek. It is so loud that two passing gentlemen hear it from the sidewalk and fetch a policeman to the house. The policeman informs them that it is Dorian Gray's residence, and the men walk away, sneering, without reporting the scream. The servants cannot open the locked door of the attic, so they manage to climb in through the roof. They find the body of a "withered, wrinkled, and loathsome" man, lying on the floor with a knife in his chest. They only recognize their master from the rings on his fingers.
While thinking of Hetty, Dorian remembers telling her that he was a very wicked man, to which she responded that "wicked people were always very old and very ugly." Like the shallow people of Dorian's class, the "pure" Hetty assumes that appearance is everything. While this superficiality is precisely what allows Dorian to win so many hearts, it also prevents anyone from truly knowing who he is.
Dorian resolves to undo his past, to block it from his thoughts, and to focus on ensuring a positive future. He crushes the mirror given to him by Lord Henry, a symbolic rejection of his own vanity and the corrupting influence of Henry's friendship. He desperately clings to his treatment of Hetty as an indicator that it is possible to cleanse his soul, but it is too little, too late. Even this seemingly conscientious gesture was committed out of the hedonistic desire to experience an unfamiliar sensation, and the vain wish to improve the appearance of his soul, as depicted in the portrait. Vanity, not morality, drove his action, proving once again that Dorian is a condemned soul.
When Dorian kills himself by trying to destroy the painting, the picture and the man once again trade appearances. The man in the portrait becomes young and beautiful, while the real Dorian becomes old and disfigured by guilt. Dorian has unwittingly realized the fear he had upon first seeing the painting: that he would wither and die, while the painting would remain young and beautiful forever. Furthermore, since the painting has been restored to its original appearance, the masterpiece of Basil Hallward is returned to the world. Dorian, seeing the knife, thinks that "As it had killed the painter, so it would kill the painter's work" (177), but the work and the painter are instead granted the immortality of artistic greatness, while Dorian himself is destroyed.
The weapon used by Dorian is the same one he had used to kill Basil. Ironically, Basil offered to destroy the painting with a knife as soon as he sensed Dorian's negative reaction to it (chapter 2), but Dorian's newfound vanity and appreciation for artistic beauty prompted him to throw his own body in front of the image. Eighteen years and eighteen chapters later, Dorian decides to do precisely what he had prevented from happening, and once again his body throws itself before the painting, subject to the dangers of its beauty.