Conan searches for clues to who murdered the Headmaster busily and finally figures out the trick that was used:the killer swam underneath the bridge and stabs the victim and ties him in a complicated fisherman's knot that when the waterwheel turns, the body would be lifted up to the ceiling of the beam that would make it look like a suicide. The suspect's reason for killing the Headmaster is to stop him from officially announcing his son, Roichi, from becoming the next Headmaster, which he claims the Headmaster betrayed him since they were selling counterfeit expensive ceramics for the past ten years.