Signal: Choki Mikaiketsu Jiken Sosahan

Fifteen years ago, a female child was kidnapped on the way from school. At that time, Saegusa Kento, who was a first-grader in elementary school student, witnessed the girl being taken away. A few days later, the girl was found in the dead, and detectives Ooyama Takeshi and Iwata Kazuo continued to investigate the crime but the culprit was not found. As time went by, Kento started distrusting the police. Fifteen years later, Kento is now a police officer and criminal profiler. One day, Kento finds a walkie-talkie that allowed him to get in contact with the past Takeshi. Police officers Kento, Takeshi, and Misaki then set on a journey to solve cold cases. (Source: Written by MyDramaList)