Got this from wikipedia
Case Closed, also known as Detective Conan (名探偵 コナン Meitantei Konan?) in Japan and other countries, is a detective manga and anime series by Gosho Aoyama which has been published in Weekly Shōnen Sunday magazine since 1994.
The series depicts the cases of a young private detective who was inadvertently turned into a prepubescent boy by a certain criminal organization. Although his body has been shrunk, he continues to solve many cases and is struggling to solve the mysteries of the criminal organization responsible in order to return to his normal body.