The Pretty Boy Detective Club obtains an invitation to a mysterious casino called Reasonable Doubt. When they arrive at the casino, they find that all the patrons and employees appear to be middle school kids. The manager of the casino, Lai Fudatsuki, challenges Nagahiro Sakiguchi to a showdown, and if Nagahiro wins, he acquires the right to operate the casino!

The artist who created the paintings found in the attic was a former art teacher named Kowako Towai. She was a suspect in a kidnapping case that happened seven years ago. How will the Pretty Boy Detective Club solve the mystery of the thirty-three paintings in the attic and the kidnapping case?

With the help of Odoru Sotoin, Manabu Sotoin's older brother and the founder of the Pretty Boy Detective Club, Mayumi steadily gains more supporters in the election. However, the Detective Club is unable to solve Wana Nagawa's hit-and-run case, let alone find any clues. The culprit behind the hit-and-run case is now targeting Mayumi and...!?