During the lunch break of the National High School Spring Kendo Tournament Heiji is attending, referee Nukitani has his throat slashed, and Nenji, Tsuneyuki, and Akane, who were in the bathroom near the crime scene, are the three suspects in the case. Detective Sato examines their belongings, but she's unable to find the box cutter that is the murder weapon. Based on the suspects' possessions, new testimony from Katsunari, the blind old man at the crime scene, the kendo uniform worn by the culprit, and information from the forensics team, Heiji determines who killed Nukitani and what they used to kill him...