The past and the present collide through a powerful walkie-talkie. Park Hae Young (Lee Je Hoon) is a police lieutenant who is an expert criminal profiler. Hae Young went into police work despite his deep-rooted mistrust of cops stemming from a traumatic event from his childhood. When he was young, his friend Yoon Jung was kidnapped and later found dead. Hae Young saw a woman pick up Yoon Jung from school on the day that she went missing, but the police would not believe Hae Young and stated that a man took her. The case remains unsolved to this day. Now working at the same police station where Hae Young tried to get the cops to believe him as a child, Hae Young walks out of the station one day and hears someone talking to him. He searches around and finds a walkie-talkie with the voice of police detective Lee Jae Han (Cho Jin Woong) talking to him. But Jae Han is from decades into the past, and he is investigating the murder of Hae Young’s friend Yoon Jung. Cha Soo Hyun (Kim Hye Soo) was a rookie during Jae Han’s time and is now an experienced police detective. Can this unexpected trio help each other solve cold cases from the past by communicating through the walkie-talkie? “Signal” is a 2016 South Korean drama series directed by Kim Won Suk. The series is based on a real-life crime spree that took place between 1986 and 1991 where 10 women were raped and murdered in the same geographic area in South Korea. The 2003 film “Memories of Murder” and the 2014 television drama “Gap Dong” also were based on the same events.