Set towards the end of the Joseon era, Sung Yi-Gyeom 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-Gyeom 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-Gyeom. Park Chun-Sam is Sung Yi-Gyeom’s servant. Park Chun-Sam is talkative, affectionate, and tearful.
Meanwhile, Sung Yi-Beom is Sung Yi-Gyeom’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-Gyeom.
In the present day, Jang Bong Hwan works as a chef at the President's Blue House. He has a free spirit, but his spirit somehow finds its way into the body of Queen Kim So Yong in the Joseon period.
King Cheol Jong has secrets. He seems like a figurehead, who is gentle and easygoing. In fact, he hides his strong aspects. Queen Sunwon is the late King Sunjo’s wife. She wields the true power in the country and, thus, relegates King Cheol Jong as just a figurehead. Kim Jwa Geun is Queen Sunwon’s younger brother. He is extremely ambitious.
Dong Baek has an extraordinary ability. He can peer into the memories of whoever he touches. With his supernatural power, get it done attitude, and eye-pleasing looks, he is fervently revered worldwide as a superstar detective. However, when his punches meet with suspects before words, he can be a bit of a headache to his comrades. Starting from the age of twenty, Han Sun Mi is the youngest to have passed the bar exam, obtain a doctorate in criminal psychology, and become a senior superintendent in the police force. Having solved five cold cases that even a detective with supernatural powers couldn't do, she is a genius profiler. She has a secret that drives her to do what she does. These two highly-skilled professionals meet their match—a serial killer with abilities that transcend theirs combined. It's going to be a fight worth watching.
Adapted from the webtoon of the same name by Jae Hoo.