The series "Yooryungeul Jabara" is a Korean detective story about the secrets of the Seoul subway. A mysterious and brutal serial killer appears in the underground, quickly earning the nickname "Metro Ghost." The investigation is led by Senior Inspector Ko Ji Sok, but the criminal literally taunts him. He disrupts the celebration dedicated to the 30th anniversary of the subway police. Meanwhile, a young girl named Yu Ren comes for an interview at Ji Sok's department. She wants to become a police officer in order to find her sister.