Signal

Park Hae-young, a present-day criminal profiler played by Lee Je-hoon, starts receiving mysterious radio transmissions from Lee Jae-han, a detective from the 1980s played by Cho Jin-woong. Through an old walkie-talkie they trade case facts and instructions, coordinating across decades to reopen cold cases that were buried by time and bureaucracy. Kim Hye-soo’s Cha Soo-hyun, a seasoned investigator tied to past tragedies, pieces together how those conversations change unfolding events. The series balances police procedure with a slow-burn mystery, as the team presses against institutional resistance while trying to prevent further tragedies, all without revealing later twists or the ending.

Created by Kim Eun-hee and Kim Won-suk, Signal premiered in 2016 and blended genre elements of crime, mystery, and speculative time communication, standing out in contemporary Korean television.

The show’s walkie-talkie mechanism and tense cross-era exchanges became a cultural touchpoint, spawning fan theories and wide discussion online. Memorable scenes and character beats entered discussions beyond typical crime drama circles, and the series is often cited when people talk about genre-bending Korean TV storytelling.

Critics and audiences praised Signal for tight plotting, morally charged themes, and strong performances, reflected in a solid average rating of 8.2 out of 10 from viewers. The writing keeps procedural detail so the stakes feel real, while the time-crossing element raises questions about accountability, institutional failure, and what justice requires. Lead actors are frequently singled out for bringing restraint and intensity, helping the show feel urgent without resorting to melodrama.