The protagonist of the Korean detective series "Royal Secret Agent" is a young heir of a nobleman named Song Yi-gyeom. One day, he is arrested by the police for engaging in gambling, which is considered inappropriate for a nobleman in the country. As punishment, he is sent to serve in the government. From that day on, he becomes a secret inspector of the imperial family. His partner is a talented girl named Hong Da-in, who has a whole network of spies. Together, they must fight corruption and punish criminals.