HONG Gildong is an infallible private detective with an exceptional memory and quirky personality. While chasing the only target he failed to find, he gets entangled in a much bigger conspiracy than he bargained for.

Chul-Soo (Hong Jong-Hyun) is the only son of a legendary thief family. He falls in love with Young-Hee (Jin Se-Yun) who is a police officer. Her family is also a police family. To get her parents permission to marry, Chul-Soo undertakes an exam to become a police officer, but both families work to prevent their marriage.