Signal

Synopsis

Park Hae-young is a cynical profiler with the Seoul police who lost faith in the justice system after the kidnapping of a little girl in his neighborhood as a child was never solved. One night, he receives a call on an old walkie-talkie that belonged to Lee Jae-han, a police detective who disappeared in 2000. Through this device, Hae-young can communicate with Jae-han in 1989 — fifteen years in the past.

The two officers, separated by time, begin collaborating to solve cold cases that never found answers: kidnappings, serial murders, covered-up police corruption. Each piece of information shared between the two eras modifies the present, creating new temporal ramifications with unpredictable consequences. Changes to the past save lives but threaten others, and Hae-young discovers that his interventions progressively alter his own history.

Cha Soo-hyun, Hae-young's superior in the present and Jae-han's former colleague in the past, becomes a crucial link between the two eras. The three characters are connected by a central case: the unsolved murder that made Jae-han disappear in 2000. Solving this mystery could save Jae-han's life — or destroy the present Hae-young knows.

Themes and Influence

Signal draws from real unsolved Korean criminal cases, notably the Hwaseong serial killer and the Bangbae-dong kidnapping, using fiction to interrogate the flaws in the Korean justice system. The drama explores the persistence of memory, responsibility toward past injustices, and the time paradox as a metaphor for the consequences of our choices. The work was unanimously hailed as a crime genre masterpiece and launched screenwriter Kim Eun-hee's career — she later created Kingdom. Signal inspired a Japanese remake (2018) and remains an essential reference in Korean thriller television.