Set during the Joseon Dynasty, the story follows Lee Gyeom, a nobleman's son who witnesses the brutal murder of his family due to a political conspiracy. After losing his memory and being adopted by a thief, he grows up as the reckless and carefree Yong. As fragments of his past return, he adopts the persona of 'Iljimae,' a masked vigilante who robs corrupt government officials to expose their crimes and aid the impoverished citizens. As Iljimae becomes a folk hero, he navigates a complex web of political intrigue, forbidden romance, and a quest for vengeance against the king and the powerful officials responsible for his family's downfall. The series masterfully balances high-stakes action with emotional depth, exploring themes of justice, identity, and the struggle against systemic corruption in a rigid social hierarchy.