William Wilson, a corrupt young aristocrat, has always been harassed by his double. Since he was a child, this homonymous character has turned up preventing his faults and condemning his evil actions. The film starts in Rome when - after a flashback recalling the unwanted intruder, Wilson is to carry out one of his deeds: to seduce a young duchess married to his enemy. William tries to lure his hated pursuer, who eventually becomes visible at Duke di Boglia's masked ball and is arrested. In one of the deserted chambers of the palace Wilson challenges his double to engage in a sword fight.