Kobato and Osanai made a pact to lead a quiet life as regular students upon entering high school. However, soon after, a handbag mysteriously disappears at the school, and Kobato is asked to help solve the case.

Kobato and Osanai are invited to Dojima's house, where he makes them cocoa using his special method. When Osanai leaves, Dojima asks Kobato about his change in personality.

During a class assignment, a vase in the cabinet seemingly breaks by itself, but there's an elaborate plan behind it. However, this mystery is quickly forgotten when Osanai sees the bicycle thief again and plots revenge.

Kobato, along with Kengo, tries to get to the bottom of Sakagami's motives. It seems there is more to the case than initially suspected. However, Kobato's concern for Osanai is also growing.

Kobato finds Osanai crying in the school hallway, but she runs away without telling him what happened. At the student newspaper club, a new mystery involving Berliner Pfannkuchen (jelly doughnuts) awaits him.

Osanai ropes Kobato into her plans for the summer vacation. However, the cake he is supposed to buy for her proves to be irresistible, even for Kobato.