Finally, Ryung and the Subway Ghost come face to face. As his rage explodes, the Subway Ghost attacks Ryung, but another tragedy puts a stop to his actions in the end. Meanwhile, Jin appears at the scene, only to run away amidst the chaos. Ryung, the Subway Police, and Ma Ri’s team put in all their efforts into reuniting the twin sisters.
Ryung and Ji Seok make their way into Kyung Hee’s house and find a room that looks like a young girl’s. After sharing the new evidence with Ma Ri and her team, they split up into two groups to chase both Kyung Hee and Yi Joon. Meanwhile, Ryung’s hopes of finding Jin alive begin to grow and Ji Seok gets a call from the hospital about his mom.
The police believe the Subway Ghost is in a mental hospital and that he plans to commit another murder. They chase him down and search the entire hospital building. Amid the chaos, Ji Seok’s mom and her caretaker are nowhere to be found. The Subway Ghost leaves behind a video clip, revealing himself and the shocking truth.
Ji Seok and Ryung catch the remaining Grasshopper who everyone believes is the Subway Ghost. However, while being interrogated, the Captain of the Grasshoppers makes a shocking statement. The truth about the Subway Serial Murder Case finally begins to reveal itself and Ryung is hopeful that she may find out what happened to her sister.
One of the Grasshoppers gets away from the police. The other two Grasshoppers confess that they only know him as Han Tae Woong, although that name turns out to be a fake identity. The investigation reaches a dead end and Ji Seok is about to be reassigned to a remote island. Ryung comes up with a plan to save Ji Seok and to catch the Subway Ghost.
The police make headway on the Subway Serial Murders and narrow down the suspect list. After getting a tip about the identity of one of the Grasshoppers, Ryung and the Metropolitan Detective Division chase him down as he might be the Subway Ghost. Meanwhile, Ji Seok’s investigative instincts start acting up again, despite his suspension.
Ryung and Ji Seok work together to save Jung Hoon and catch the kidnapper. With their great partnership, they discover the identity of the person who helps the kidnapper hide from the police. Meanwhile, the Subway Ghost marks his next target and Ryung activates her subway search skills to track him down.
Ryung and Ji Seok save Choi Do Chul just in time. Throughout their investigation, Ji Seok miraculously learns to appreciate Ryung’s over-the-top nature. Meanwhile, a star professional fighter becomes the PR Ambassador for the Subway Police. By chance, Ryung comes across his dirty secret and the Wangsoori Subway Police finally get a lead on the Grasshoppers.
Ryung and Ji Seok attend the disciplinary committee hearing and return to the station for night duty. Thanks to Ji Seok’s martial arts demonstration and a pot of noodles, Ryung gets her hands on the screen door keys once more. Meanwhile, an ordinary father, whose livelihood takes place on the subway, goes missing.
The Subway Police of Wangsoori Station is led by Chief Inspector Ko Ji Seok. He is the best of the best, although his only goal in life is to have a stable, uneventful career. However, a serial killer, nicknamed “the Subway Ghost”, strikes the Subway Police 30 Year Anniversary event. An applicant shows up for a job interview to join the team.
A romantic investigative drama about rookie detective Yoo-Ryung who solves cases with her overflowing sense of justice and exceptional spatial perception but always gets herself into trouble because of her rash actions. She meets the Wangsimni station constabulary chief, a man who avoids cases and seeks stability who always ends up cleaning up after the problems caused by Yoo Ryung and holds the key to solving the cases.