Conan finds Hiramune murdered with the letter "Z" burned into his back. The police department arrive and are confused as the letter they were expecting was "N" as the previous victims had the letters "E", "S", "W" and were thought to be Cardinal direction. They notice the Hiramune's left hand was on his keyboard on the keys "Ctrl" and "C" and his right hand holding the wire of his mouse. Takagi and the Junior Detective League decide to accompany him and his interrogation of the victim's relatives. Conan than realizes the victims share one thing in connection, Mahjong.