SYNOPSIS

Park Hae-young (Lee Je-hoon) is a criminal profiler and also a police lieutenant. Even though he is a cop, he doesn't trust cops due to his own past experience. One day, Hae-young hears someone talking through an old walkie talkie. This mysterious guy helps Hae-young to solve the cold cases. And Hae-young’s team leader, veteran detective Cha Soo-hyun (Kim Hye-soo) thinks this guy who is from the past is Lee Jae-han (Jo Jin-woong), her senior cop and first love, who died 15 years ago…