The Moon Flows Over the River tells the story of the soul exchange between a prince who has lost his smile and a saddle-carrying merchant who has lost her memory. Joseon Crown Prince Lee Gang, who lost his crown princess, gave up his own happiness and only thought about revenge. When Lee Gang's long-planned revenge plan finally took the first step, he met the saddle-carrying merchant Park Dal Yi who looked exactly like the deceased crown princess, and exchanged bodies for unknown reasons, falling into a series of chaos.