Kento (Kentaro Sakaguchi) is only a child when he witnesses a mysterious woman kidnapping a young girl who is then later murdered. Although he informed the police of what he saw, no one took him seriously. Fifteen years later, Kento is a police officer and can't forget what he witnessed as a child. Still a cold case, Kento believes that it'll never get solved as the statue of limitations is about to run out. That is until he hears a voice on an abandoned radio of someone who is also investigating the case. When these two pair up, will they be able to solve the fifteen-year old murder before time is up? "Signal" is a 2018 Japanese drama based on the 2016 Korean drama of the same name.