Han Tae-joo (Jung Kyung-Ho) is a modern-day forensics scientist who leads a crime investigation team in 2018. He has risen up the police corporate ladder rapidly by trusting data over anything else. One day, while investigating a serial murder case, he met with an accident.

When Tae-joo wakes up from unconsciousness, he finds himself in 1998, 20 years back. This is the year of the 1998 Seoul Olympics. He does not know why he is there.

Thrown into an unfamiliar world, he tries to look for clues to find out why he is now 20 years back into the past. There, he also met his own family, including himself when he was a little boy.

He is now a police detective, appointed to work at a police station in a small city.

He is part of a police investigation team that includes the following:

• Kang Dong-chul (Park Sung-woong). Dong-chul is the head of the homicide team and is a police detective who is not interested in evidence and instead uses his instincts and intuition to solve cases.
• Yoon Na-young (Go Ah-sung). Na-young is a passionate female ace police detective who dreams of becoming a star detective. She also happens to fall in love with Tae-joo subsequently. Will they get together in the end?
• Lee Yong-gi (Oh Dae-hwan). Yong-gi is a police sergeant in the homicide team and has a hot temper.
• Jo Nam-sik (Noh Jong-hyun) is the youngest police detective in the homicide team.

To get back to the present day of 2018, he tries to solve a serial murder case. In 1998, he finds some traces of the serial killer that he is pursuing in 2018.

Is this serial killer the same man that he is looking for in 2018?

Why did Tae-joo go back to 20 years ago, 1998?

Did he manage to go back to 2018? Or did he remain there in 1998?