Synopsis
A criminal profiler Park Hae Young (Lee Je-hoon), solves a kidnapping case that ended up with a falsely accused who apparently disappeared after the crime, with a mysterious walkie-talkie he picks up. The success of this case triggers the formation of a long-term cold case team, led by Detective Cha Soo-Hyun (Kim Hye-soo), who has been searching her long-lost mentor Lee Jae-Han (Cho Jin-woong), for the past fifteen years. With the help of Detective Lee Jae-Han, the person at the other end of the walkie-talkie, Park Hae-young solvesother cold cases that have remained unsolved for years, while helping Lee Jae-Han help solve some cases in the past. Grave unintended sequences follow.