During the Joseon Dynasty, the Secret Royal Inspectors are the eyes and ears of the king. They travel the provinces undercover and listen to the plight of the common people, investigating abuses and corruption of government officials.
Set at the end of the Joseon era, Seong I Gyeom, a recent top scorer in the state exam, lacks ambition despite his success. After being caught gambling, he is assigned as a Secret Royal Inspector to expose corruption. Alongside fellow inspector Hong Da In and his talkative servant Park Chun Sam, I Gyeom investigates cases. His family, including his noble father, stepmother, slave, and younger stepbrother Seong I Beom, faces tension as I Beom is barred from inheritance due to his mother's low status, fueling resentment toward I Gyeom.