Case closed - Gosho Aoyama

When ace high school detective Jimmy Kudo is fed a mysterious substance by a pair of nefarious men in black--poof! He is physically transformed into a first grader. Until Jimmy can find a cure for his miniature malady, he takes on the pseudonym Conan Edogawa and continues to solve all the cases that come his way.

At long last, Conan has located the scientist responsible for the formula that turned him into a kid. Trouble is, she's taken the formula herself, and she can't change back! Together, Conan and the diminutive doctor track down a floppy disk that may contain the secret to curing their condition, only to find the former owner crushed under a fallen bookshelf. Can they crack both the locked-room mystery andthe locked disk?