Set towards the end of the Joseon era, Sung Yi Gyum placed first in the state examination and he now works at the Hongmungwan (administrative and research department). He doesn't have a goal or ambition for his life. One day, Sung Yi Gyum is caught gambling. As punishment, he is assigned to work as a secret royal inspector. His job is to eradicate illegal acts and corruption by public officers. He carries out his new job with the help of Hong Da In and Park Chun Sam. Hong Da-In is a female inspector and solves cases with Sung Yi Gyum. Park Chun Sam is Sung Yi Gyum’s servant. Park Chun Sam is talkative, affectionate, and tearful. Meanwhile, Sung Yi Bum is Sung Yi Gyum’s younger stepbrother. His father is a nobleman, but his mother is a slave. Due to his mother's low social status, his father does not accept him as his real son and he is barred from having certain opportunities. He opposes his older stepbrother Sung Yi Gyum.
