Signal

Hae-young finds an old walkie-talkie in the corner and gets clues on the unsolved kidnapping case.

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.

Hae-young joins the unfinished case squad and Jae-han says something through the walkie-talkie.

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.

Hae-young is confused after discovering that the talks through the walkie-talkie changed the past.

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.

The squad starts investigating the Gyeonggi Nambu case despite the opposition from their superiors.

Hae-young starts to investigate Jae-han's disappearance. Jae-han's former colleagues get suspicious about seeing Hae-young digging into the past.

Hae-young gets one step closer to the truth of the disappearance of Jae-han.

Seeking vengeance for the events that led to the death of his daughter, Kyung-tae commits a kidnapping after getting out of prison for burglary.

Hae-young continues to make an effort to change the wrongly intertwined past and future.

After Su-hyeon dies, Hae-young contemplates whether he should keep the walkie-talkie.

Soo-hyun and Hae-young notice a connection between the burglary case and Da-hye, the woman who killed herself twenty years ago.

After checking the fingerprint of Da-hye, the squad tracks down the whereabouts of her.

Hae-young suspects Chi-soo who might have something to do with the disappearance of Jae-han.

Through a walkie-talkie, Jae-han realizes that Su-hyeon and Hae-young are on the same team.

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.

Jae-han heads to In-ju to investigate the In-ju female student sexual assault case.

Hae-young becomes a suspect for the murder of Chi-soo. Jae-han realizes who the principal offender of the attack on Hye-seung is.

Su-hyeon falls in great shock after finding out that Chi-soo killed Jae-han.

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.

Jae-han heads to In-ju and finds out that Hae-young is Seon-woo's younger brother.

Hae-young heads to In-ju and interrogates the person who pointed at his brother as the main culprit.

With Seon-woo's death coming close, Jae-han hurries to In-ju to save Hae-young's brother.

Hae-young does not lose hope of saving Jae-han and immediately grabs the walkie-talkie.