Signal is a 2016 drama that is a combination of several genres including mystery, thriller, crime, with a hint of fantasy. What made it so captivating is the fact that the cases used in the series were based on actual crimes and tragedies that occured in South Korea. 

The story starts when Park Hae-young (Lee Je-hoon) accidentally finds an old walkie-talkie, without any battery in it. But strangely, the walkie-talkie can still be used. Through the walkie-talkie, Park Hae-young was able to communicate with a detective Lee Jae-han (Cho Jin-woong) in 1989. He was one of the senior police officers at that time.

It turns out, the walkie talkie now in Park Hae-young’s possession was Lee Jae-han’s own. He accidentally found it when it was about to be disposed of when it suddenly made the sound of Lee Jae-han’s voice. Besides turning on without any batteries, what’s even stranger is that Park Hae-young heard Lee Jae-han’s voice in 2015, but Lee Jae-han is sure that he is in 2000.

This unusual correspondence, which is only limited to a few minutes each day, opens a can of worms. Now with the power of foresight and hindsight, Park Hae-young and Lee Jae-han, along with Cha Soo-hyun (Kim Hye-soo), are in a race against time to solve crimes or prevent them from happening. However, they will learn along the way that changing certain elements in the past can have dire consequences in the future.