The members of the Pretty Boy Detective Club: Manabu Sotoin, Nagahiro Sakiguchi, Michiru Fukuroi, Hyota Ashikaga, and Sosaku Yubiwa, along with Mayumi Dojima, visit the location where she saw the lost star ten years ago. The deadline imposed by her parents to stop searching for the star is quickly approaching. Meanwhile, she finds herself being tailed by a shadowy figure! She escapes from its evil clutches only to be told a shocking truth from the Pretty Boy Detective Club...

On their way home from school, Mayumi Dojima and Manabu Sotoin are abducted by a group that call themselves the Twenties. They are after a secret hidden within the star that Mayumi saw ten years ago. The remaining members of the Pretty Boy Detective Club take action to save their friends and finally face the Twenties in a battle! What will Mayumi’s decision be after the search for the missing star ends?

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?