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.

There will be a change of pace in the school newspaper. Kobato shows an interest in serial fires.