Season 1
🎬 16 Episodes 📅 2016 ⏱ 89 min Ongoing 🔄
A haunting transmission bridges two detectives across twenty years, connecting present-day investigators with their predecessor through an old walkie-talkie called Signal. As they piece together a decades-old cold case, the line between past and present blurs dangerously. Each revelation deepens the emotional weight—solving the crime means confronting sacrifices made and lives altered forever. The question becomes not just who committed the crime, but whether changing the past can heal the present.
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📊 Season Stats
16
Episodes
2016
Year
89
min / ep
23.7
Watch Hours
1/1
Season No.
⭐ 8.6
Best Episode
Ep. 8 · How Are You Alive?
Ongoing 🔄
Status
🎬 Season Trailer
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🎬 Episodes 16 episodes
1
⭐ 8.4
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.
🎬 Kim Won-suk
2
⭐ 8.2
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.
🎬 Kim Won-suk
3
⭐ 8.0
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.
🎬 Kim Won-suk
4
⭐ 8.0
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.
🎬 Kim Won-suk
5
⭐ 7.5
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.
🎬 Kim Won-suk
6
⭐ 8.0
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.
🎬 Kim Won-suk
7
⭐ 7.8
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.
🎬 Kim Won-suk
8
⭐ 8.6
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.
🎬 Kim Won-suk
9
⭐ 8.4
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.
🎬 Kim Won-suk
10
⭐ 7.8
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.
🎬 Kim Won-suk
11
⭐ 7.8
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.
🎬 Kim Won-suk
12
⭐ 8.2
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.
🎬 Kim Won-suk
13
⭐ 8.0
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.
🎬 Kim Won-suk
14
⭐ 8.0
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.
🎬 Kim Won-suk
15
⭐ 8.0
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.
🎬 Kim Won-suk
16
⭐ 8.4
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.
🎬 Kim Won-suk