Ryota Tachibana started a local grocery store after getting fired from the supermarket where he worked due to an erroneous order. At the mansion he visited on request, he encountered the murder of a famous painter, Shinomiya, and was dressed in a murderous robe. In front of Ryota in such a big pinch, Arisa Ayaragi, a beautiful girl dressed in Lolita clothes and calling herself a detective, appears... A masterpiece humor mystery in which the young lady of the detective family and Ryota challenge a difficult case!

Reiko is a rich heiress to a zaibatsu, but she chose to work as a detective. She resents her superior, Kazamatsuri, who always seem to be making illogical deductions that causes murder cases to become cold cases. One day, her butler suddenly announces his retirement, and he chooses Kageyama as his replacement. Reiko realizes that Kageyama's deduction skills are very good after Kageyama solved a seemingly unsolvable mystery. After that, whenever Reiko meets an unsolvable case, she would lay out the details of the case for Kageyama, and he would explain to her how that particular case is solved after dinner. After every case, Kageyama also explains to Reiko some universal truth or human nature that led to each crime being committed. (Source: Wikipedia)

For some reason, there are many incidents around Kirigamine Ryo, the deputy director of the detective department at Koigakubo Gakuen High School. The thief who disappeared from the school building, the relationship between the classmate and the poisoned coffee clan, the UFO turmoil of out-of-school learning-Ryo is enthusiastic about solving it, but the gag is just clear and the reasoning is developing. Is it the deputy director of the detective department who will show off the good reasoning? What is the end of the humor school reasoning?