Signal

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

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

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.

Hae-young learns that Chi-soo and Jae-han met in 1999 during a case in Inju. After serving time for the crime, Hae-youngs brother had killed himself.

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.

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.

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-woos death.