Insurance Investigator Cha Yeon-ho (Lee Min-ki) is accidentally caught up by the Traffic Crime Investigation Team (TCI) during a "Car Fraud" gang bust. During questioning he shares his case records of a possible Vehicular Serial Murder case with Lieutenant Min So-hee (Kwak Sun-young). So-hee gets personally involved after she finds out an acquaintance may have been a victim.

Killer Jung Ho-kyu (Bae Yoo-ram) plots his revenge against Jo Seok-tae (Lee Do-goon) for aiding Lt. Min So-hee. Investigator Cha Yeon-ho obtains damaging evidence against Ho-kyu. Yeon-ho gets labeled as a whistle blower and quits his job. Capt. Jeong Chae-man (Heo Sung-tae) of TCI hires him into the team as a Lieutenant due to his investigative expertise.

TCI’s investigation into ghostly apparitions causing vehicular accidents uncovers a multiparty Car Scam Ring affiliation. So-hee’s father, Min Yong-gun (Yoo Seung-mok), shares some of her background story with Yeon-ho. Yeon-ho and So-hee go undercover as husband and wife.

The TCI investigates the case of a woman jumping from a car. The Joint Investigative Unit moves to Namgang Police Station and takes over TCI’s case. Cha Yeon-ho is disgraced when a culprit gets away. So-hee decides to give him personal training in the finer arts of police arrest techniques.

The Hit and Run Case sheds light on a Car Thief and Serial Rapist case. Mysterious envelopes related to Cha Yeon-ho’s tragic past traffic accident appears. Min So-hee may be a little over zealous in the police arrest techniques training. Yeon-ho confronts Deputy Commissioner Pyo Myung-hak (Heo Jung-do) who investigated his case in the past.