Born from a tryst between a nobleman and a slave woman, Hong Eun Jo is no stranger to the plight of the average person, especially after her father fell ill. By day, Eun Jo works as a doctors, but by night, she assumes the identity of "Hong Gil Dong," a thief who steals from corrupt officials to spread wealth among those in need. Hong Gil Dong's antics attract the attention of Prince Yi Yeol, who has a penchant for investigations and is personally intrigued by the mystery of the righteous thief, although most palace officials believe that he's just joking around. Amidst his search, Yi Yeol runs into Eun Jo, falling in love at first sight – but when Yi Yeol and Eun Jo happen to swap bodies, secrets they both try to keep hidden risk getting out.