1. 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 — Season 1
Communicating via a walkie-talkie that transcends time, a profiler from 2015 and a detective from 1989 join forces to tackle crimes and injustice.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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.
9. 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.
10. 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.
11. 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.
12. 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.
13. 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.
14. 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.
15. 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.
16. 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.