After being attacked by assassins and falling off a cliff, crown prince Lee Yool (Do Kyung Soo) loses his memory and suddenly becomes the good-for-nothing Won Deuk. He gets taken in by a smart girl called Hong Shim (Nam Ji Hyun) who mistakes him for her fiancé. The two soon marry due to a decree that Lee Yool himself had issued earlier mandating that all single people get married! As Lee Yool struggles to adjust to marriage and commoner life, the secret behind the attack also gradually comes to light. What challenges will the couple face when Won Deuk goes back to the palace and they realize their true identities?