Lee Yul is the Crown Prince of Joseon, a perfectionist who disregards the majority of those in the royal palace and appears cold and demanding when in reality, he is just lonely. One day, he passes a law stating that all Korean citizens of marriageable age must do so before they reach the age of 28. Hong Shim is a strong, intelligent woman who takes on multiple jobs to support herself and her father. She is also the oldest unmarried woman in her village and is in need of a husband in order to avoid punishment from law officials. In an attempted assassination, Lee Yul finds himself severely injured and under Hong Shim and Hong Sim's father's care. Due to his injuries, Lee Yul develops temporary amnesia and wanders around aimlessly as a commoner with no name or identity. Because of the law passed by Lee Yul, he and Hong Shim are forced to marry each other in order to save Hong Shim from punishment as well as her village from the drought. What follows is the love story of Hong Shim, 'Joseon's oldest unmarried woman,' and Lee Yul, the amnesiac Crown Prince.