As the narrator, an "outcast among outcasts," begins to recount his story, he cautions the reader that "William Wilson" is not his real name; he doesn't want the page to "be sullied with my real appellation." The miserable man tells of his childhood and his life at school, where he encountered another boy who looked exactly like himself and had the same name and birthday.

All the children at school recognized the narrator's preeminence among them, except for this strange double. While the first William Wilson was aggressive, witty, and imperious, the double presented himself as quiet, gentle and wise--but unthreatened. In the end their feelings towards each other "partook very much of positive hatred."

Many years later, as the narrator was busily engaged in cheating at a game of cards, the second William Wilson suddenly appeared out of nowhere and revealed Wilson's scam to everyone present. Subsequently, time after time, just as Wilson was about to achieve some nefarious end, this anti-Wilson unerringly stepped in and destroyed Wilson's chances.

The last straw occurred in Rome during Carnival; just as Wilson was about to seduce a married woman, his double arrived to squelch the affair. Wilson flew into a rage and killed his nemesis, only to discover he had stabbed a mirror--but the dying image in the mirror whispered, " . . . How utterly thou hast murdered thyself."