And Then There Were Two — Gosho Aoyama

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 and the locked disk?