Showdown! The Cutthroat Who Crossed Through Time!!.Kyu discovers the key to the store room inside the room, making it a double-locked-room mystery. The classes are trapped there by a storm. Dan asks the students to help out with resolving the mystery. They find that the kitchen has been ransacked, and Kazuma finds something to form a theory to solve the double-locked-room mystery. Unfortunately this theory fails, but not before giving a clue to Ryu. Later that night, Kyu hears a knock on his door, and is joined by Kinta as they follow a trail of muddy shoe prints leading to a room where Shishido lays murders, his body also split into parts.