Season 1

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.

Cha Yeon-ho is interrogated in regards to his past vehicular homicide case. When Director General Lee Tae-joo (Oh Eui-sik) of the Joint Task Unit withholds information from his team and the TCI, they go to the aid of TCI.

Pyo Myung-hak is promoted to Commissioner General. TCI’s investigation into a car carrier trailer rollover case finds that it was malicious and caused the death of a man driving home. Yang Jae-young (Heo Ji-won), the son of a former gangster, is murdered. Eo Hyeon-gyeong (Choi Moon-hee) meets Woo Dong-gi’s (Lee Ho-cheol’s) father, Woo Gil-soon (Joo Hyun).

TCI reveals a serial pattern in the Car Carrier Trailers Rollover Case which affected prior truck drivers for CY Logistics. Woo Gil-soon was one of them. Truck driver Han Kyung-soo (Han Sang-jo) confides the names of the individuals related to Cha’s past accident and that all had received threatening mail.

TCI is assigned the Yang Jae-young Murder Case. Min Yong-gun (Yoo Seung-mok), So-hee’s father, gets involved in an accident while chasing a Hit and Run driver. Evidence leads to Pyo Jung-wook (Kang Ki-doong), the Commissioner General’s son. Yeon-ho shares his knowledge of his accident from 10 years prior with So-hee.

Cha Yeon-ho finds out that Kim Hyun-min (Kim Dae-ho), the National Forensic Service analyst is the culprit behind the threatening envelopes. Pyo Jung-wook seeks the help of former gangster Yang Seok-chang (Lee Yoo-joon), Chairman of YSC Group. Han Kyung-soo confesses who the actual culprits were in Yeon-ho's vehicular homicide case.

TCI succeeds in capturing the real culprits of the 10 year vehicular homicide, car carrier and the Hit and Run cases. During Pyo Jung-wook’s trial, Commissioner Pyo is also implicated and arrested. Conniving Lee Tae-joo is promoted to Chief Superintendent. Rather than being promoted the team is dissolved and transferred. Cha Yeon-ho is sent to remote Hwapyeong island.

When a local Inn Keeper’s daughter disappears Cha Yeon-ho reaches out for help. The old TCI gang takes vacation to assist him. The team is finally promoted with exception of Chief Jeong who had rendered his resignation. When Chief Justice Shin So-jung (Park Ji-young) is promoted to Director National Office of Investigation, she seeks out Chief Jeong to reestablish the TCI.