The film begins in 1986, with police officer Park Gwang Ho (Choi Jin Hyuk) desperately trying to catch a serial killer. He chases after the killer and goes through a tunnel. Strangely, on the other side of the tunnel, police officer Park Gwang Ho reappears in 2017. The serial killer strikes again 30 years later. Police officer Park Gwang Ho teams up with a modern-day police officer Kim Sun Jae (Yoon Hyun Min) and criminal psychology professor Shin Jae Yi (Lee Yoo Young) to catch the killer.