Gauran Sharma, Delhi: Signal, just like the drama is rightfully named, starts with a ‘signal’ in the mundane life of a hardworking man, Park Hae-young, who is a police lieutenant and an expert criminal profiler. A strange message from an abandoned walkie-talkie from the past gets him involved in a mysterious, unsolved cold case from 15 years ago. As the events unfold, detective Park, as well as the viewers, realise that the signal was not just an ordinary one.