A monkey and Aya trapped in an underground warehouse in a gymnasium where someone burned briquettes. The monkey unlocks her handcuffs with a wire that has fallen in one corner of her, even though she is stunned. Open the door closed with 10 padlocks from the outside and escape with Aya. From this situation, the monkey is inferred to be the crime of an internal human who is familiar with the school. After this, the monkey asks the members of the basketball club to tell him why the bright Aya became dark. Aya is said to have become a dark child because she was obsessed with the man she was dating. After this, the monkey who noticed the method that the criminal made the master key changes the lock of the basketball club room again in order to arrest the criminal. The criminal who appeared on the scene was an unexpected person.
何者かに煉炭を焚いた体育館の地下倉庫に閉じ込められたサルとあや。サルは朦朧となりながらも片隅に落ちていた針金を使って手錠を解錠。外から10個の南京錠で閉ざされた扉も開け、あやを連れて脱出する。この状況からサルは学校の事を熟知した内部の人間の犯行と推理。この後、サルはバスケ部の部員たちに明るかったあやが暗くなった理由を教えてもらう。あやは付き合っている男性にしつこくされ、暗い子になってしまったという。この後、犯人が合鍵を作った手口に気付いたサルは犯人を現行犯逮捕するため、再びバスケ部部室の錠前を替えるが…。現場に現れた犯人は意外な人物だった…。
