Set in 18th-century Joseon, it tells the fictional story of Crown PrinceLee Sun (Yoo Seung-ho) and his fight against the powerful and wealthy organization, Pyunsoo-hwe that controls the country behind the scenes due to its monopoly of the nation's water supply. With the help of the woman he loves named Han Ga-eun (Kim So-hyun), Lee Sun overcomes adversity and grow as a just ruler.