An unnamed narrator announces that his real name shall remain a mystery, for he wishes to preserve the purity of the page before him. Instead, the narrator asks that we know him as “William Wilson” throughout the tale of misery and crime that he is about to tell. He explains that this tale will explain his sudden and complete turn to evil.

The narrator believes that he has inherited an excitable temperament from his otherwise dull-minded parents. As a young student, he escapes from this environment, and his early memories concern a large Elizabethan house in England where he attended school. He describes the school as a Gothic prison, with a spiked iron gate that has creaky hinges. The principal, who also acts as the pastor of the church, enforces the severe rules of the school.

Despite the severity of his surroundings, the narrator emerges as a colorful student and feels a certain superiority to his classmates, with the exception of one student. According to the narrator, this student bears exactly the same name: William Wilson. This second William Wilson interferes with the narrator’s mastery over his classmates, thereby becoming for the narrator an object of fear and competition. This rivalry becomes only more pronounced for the narrator when he learns that they joined the school on the same day and that, because of the two William Wilsons’ identical builds and styles of dress, many older students believe they are brothers. The narrator’s rival even imitates his mode of speaking, except he can never raise his voice above a whisper. Nevertheless, the narrator rejects any connection between him and his rival. Despite this antagonism, though, the narrator remains on speaking terms with his competitor and admits, at first, to being unable to hate him.

The relationship soon deteriorates, however, and a violent altercation ensues between the two William Wilsons. The scuffle evokes in the narrator memories of his infancy, which makes him grow only more obsessed with William Wilson. On a night not long after the scuffle, the narrator sneaks into his rival’s bedroom to play a practical joke. Shining the light from his lamp on his rival’s face, the narrator believes he sees a different William Wilson, a face unique to the darkness. Terrified by the facial transformation he imagines, the narrator rushes from the room.

After several months, the narrator becomes a student at another school, Eton, and attempts to leave behind memories of the other William Wilson. He abuses alcohol in this effort to forget the past, and he recalls one debaucherous party in particular. In the midst of the drunken revelry, a servant announces the presence of a mysterious guest calling for the attention of the narrator. Excited and intoxicated, the narrator rushes to the vestibule, only to discover a youth of his same size and dress. The faintness of the light prevents the narrator from discerning the visitor’s face. Grabbing the narrator’s arm, the guest whispers “William Wilson” in the narrator’s ear and quickly vanishes.

Changing schools again, the narrator moves to Oxford, where he picks up the vice of gambling. Skilled at this vice, the narrator chooses weak-minded classmates on whom to prey for extravagant monetary gain. After two years at Oxford, the narrator meets a young nobleman named Glendinning and makes him his next gambling target. Allowing him to win at first, the narrator lures him with the prospect of more success to a large party he has arranged. At this party, Glendinning plays exactly as the narrator expects and quickly amasses large debts. At the moment that he quadruples his debt, Glendinning becomes ghastly pale, and the narrator realizes his triumph. Suddenly, however, a stranger intrudes on the party with a rush that extinguishes all the candles in the room. He reveals the narrator to be a scam artist and promptly retreats. The announcement ruins the narrator, forcing his departure not only from Oxford, but also from Britain.

Settling at last in Rome, the narrator attends a masquerade ball in the palace of the duke Di Broglio. The narrator secretly desires the wife of the duke, who has informed him of the costume she will be wearing. As he searches for her, the narrator feels a light hand on his arm and hears a whisper in his ear: “William Wilson.” The whisperer wears the same costume as the narrator, a Spanish cloak with a black silk mask. Drawn into a side room, the narrator becomes enraged, drawing his sword and stabbing his rival. To the narrator’s horror, the layout of the room mysteriously changes, and a mirror replaces the body of his antagonist. He stares into the mirror to find his own body stabbed and bleeding, and he hears his rival speak as though with his own voice: “In me didst thou exist—and, in my death, see by this image, which is thine own, how utterly thou hast murdered thyself.”