Profiler Park Hae-youn hears a man calling his name through a discarded two-way radio. The voice starts talking about an unsolved crime.

Solving the kidnapping draws Hae-young into the Cold Case Task Force with Su-hyun, while Jae-han from 2000 tells Hae-young something mysterious.

Hae-young is shaken after realizing their walkie-talkie conversations have changed the past. Meanwhile, Jae-han in 1989 draws suspicion because of it.

Despite opposition from superiors, the Task Force investigates the South Gyeonggi Serial Murder case and uncovers the suspect in a 26-year-old crime.

Hae-young gets closer to the truth behind Jae-han's disappearance. Meanwhile, police are in an uproar over a mysterious kidnapping that night.

Hae-young and the police locate the kidnapper and the victim. Jae-han continues trying to fix a past and future now dangerously intertwined.

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.

After finding Da-hye's fingerprint, the Task Force traces her whereabouts. In the past, Jae-han unravels the truth behind the 1995 serial robbery.

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.

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.

Hae-young asks Jae-han to reveal the truth about a case in Inju tied to his brother. Jae-han then goes to Inju to investigate a sexual assault case.

The police suspect Hae-young assaulted Chi-soo, and Su-hyun is shocked to learn that Chi-soo killed Jae-han. Jae-han investigates the Inju students.

Su-hyun anxiously awaits DNA results to see if the remains they found match Jae-han, while Jae-han learns Hae-young is Seon-woo's younger brother.

Hae-young realizes the possibility that his brother could have been murdered after learning from Hye-seung that Sun-woo was not guilty.

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.

Hae-young refuses to give up on saving Jae-han even after being shot. As 11:23 nears, Jae-han heads again to Seonil Mental Hospital.