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.

Kwon Hyuk Joon's grandfather, the head of the traditional Kwon family agrees to an arranged marriage between his grandson, Hyuk Joon, and Yoon Jung Sook when Yoon Jung Sook is born. Eventually, the two families lose contact with each other, because soon after the contract is signed, Jung Sook's family encounters financial issues and is forced to run away.

18 years later, Jung Sook has grown up to be a rebellious and strong-willed girl who just wants to live her life as she sees fit. With little aspirations, she is the direct foil of her achievement-bound counterpart, Hyuk Joon. When the two meet again, they clash horribly; Jung Sook thinks her fiancee is nothing but boring, and Hyuk Joon believes Jung Sook to be nothing but an immature child. Despite this, they marry. What follows is the story of their new life living together as a couple, and the obstacles they are faced with.