Detectives from the present and a detective from the past communicate via walkie-talkie to solve a long-time unsolved case.
Episode 1
Profiler Park Hae-young hears a man calling his name through a discarded two-way radio. The voice starts talking about an unsolved crime.
Episode 2
The statute of limitations is lifted after the suspect's arrest. Hae-young joins Soo-hyun's team for the newly established cold case squad.
Episode 3
Reality changes after Hae-young exchanges information with Jae-han. Hae-young tries to work together with Jae-han in 1989 to prevent the next murder.
Episode 4
The ninth victim is Won-kyung, the woman Jae-han loves. A driver turns himself in, but Soo-hyun and Jae-han determine that his son is the real killer.
Episode 5
Hae-young starts to investigate Jae-han's disappearance. Jae-han's former colleagues get suspicious about seeing Hae-young digging into the past.
Episode 6
Seeking vengeance for the events that lead to the death of his daughter, Kyung-tae commits a kidnapping after getting out of prison for burglary.
Episode 7
Jae-han arrests Se-kyu for the serial burglary case, but the culprit is freed after serving a short sentence; Kyung-tae still commits murder.
Episode 8
Soo-hyun and Hae-young notice a connection between the burglary case and Da-hye, the woman who killed herself twenty years ago.
Episode 9
Hae-young learns that Chi-soo and Jae-han met in 1999 during a case in Inju. After serving time for the crime, Hae-young's brother had killed himself.
Episode 10
The bodies discovered in the mountains appear to be more victims of the 1997 serial murder case. Jae-han learns that Soo-hyun became team leader.
Episode 11
Hae-young and Soo-hyun arrest Jin-woo after coming to the conclusion that he is the killer. Hae-young asks Jae-han about the Inju rape case.
Episode 12
Hae-young becomes a suspect for the murder of Chi-soo. Jae-han realizes who the principle offender of the attack on Hye-seung is.
Episode 13
Soo-hyun and the others mourn after confirming that the remains belong to Jae-han. Hae-young learns that Jae-han used to look after him in the past.
Episode 14
Hae-young realizes the possibility that his brother could have been murdered after learning from Hye-seung that Sun-woo was not guilty.
Episode 15
Hae-young is arrested for the murder of Chi-soo. Soo-hyun hears Jae-han apologizing over the radio for not being able to prevent Sun-woo's death.
Episode 16
Hae-young is in critical condition after being shot while meeting with Sung-bum. In 2000, Jae-han has been captured by Bum-joo.
