S01E01 You're Doomed
Profiler Park Hae-young hears a man calling his name through a discarded two-way radio. The voice starts talking about an unsolved crime.
Signal
There are those who are born monsters, but there are also those who are made into monsters by people.
Overview
Detectives from the present and a detective from the past communicate via walkie-talkie to solve a long-time unsolved case.
Episodes
S01E02 We Still Have a Chance
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.
S01E03 We Can Prevent the Killings
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.
S01E04 We Found the Killer
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.
S01E05 Changing the Past Alters the Present
Hae-young starts to investigate Jae-han's disappearance. Jae-han's former colleagues get suspicious about seeing Hae-young digging into the past.
S01E06 Catch Him by All Means
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.
S01E07 We Must Dig Deeper
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.
S01E08 How Are You Alive?
Soo-hyun and Hae-young notice a connection between the burglary case and Da-hye, the woman who killed herself twenty years ago.
S01E09 Hongwon Dong Case
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.
S01E10 Someone Has to Stop the Bad Guys
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.
S01E11 The One Last Case
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.
S01E12 The Case Was Manipulated
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.
S01E13 The Real Assailant
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.
S01E14 Not Now, But Maybe In The Past
Hae-young realizes the possibility that his brother could have been murdered after learning from Hye-seung that Sun-woo was not guilty.
S01E15 Is It Really You?
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.
S01E16 If You Don't Give Up
Hae-young is in critical condition after being shot while meeting with Sung-bum. In 2000, Jae-han has been captured by Bum-joo.
Cast
Lee Je-hoon
Park Hae-young
Kim Hye-soo
Cha Soo-hyun
Cho Jin-woong
Lee Jae-han
Jang Hyun-sung
Kim Bum-joo
Jung Hae-kyun
Ahn Chi-soo
Kim Won-hae
Kim Gye-chul
Jung Han-bi
Oh Yoon-seo
Lee Yoo-jun
Jung Heon-gi
Kim Min-gue
Hwang Ui-kyung
Kang Chan-hee
Park Sun-woo
Im Hwa-young
Cha Soo-min
