Shinichi Kudou is a gifted high school student, famous for successfully cracking numerous complicated cases. But when he stumbles upon two suspicious men and decides to tail them, he inadvertently witnesses a heinous illegal activity. Unfortunately, he gets caught and is administered an experimental drug by the criminals, leaving him for dead. To Shinichi's amazement, he survives the ordeal, albeit as a seven-year-old child with his intellectual abilities intact.