Meitantei Conan (2015) (Light Novel)

Widely known as "The Modern-Day Sherlock Holmes", Shinichi Kudo is doing amazing work as a high school detective. One day, he heads to an amusement park with his childhood friend, Ran Mouri. But there he spots two suspicious men in black, and sensing a case abrewing, decides to tail them. Unfortunately, one of the men quickly realizes that Shinichi is following them, knocks him out, and forces him to take poison. And when he comes to, he finds that his body has shrunk back to that of a child?! Starting that day, he took the name "Conan Edogawa" in order to not reveal his true identity even to Ran, and began solving cases as a little elementary school detective!