During a class field trip, Riiya accidentally falls off a bridge inside a cave and gets lost ashore somewhere inside the cave. A mother monster rescues him and tends to him like a baby. The Banana class searches for him and finds the mother monster and thinks she will hurt Riiya. They scare the monster away, hurting her feelings. After a long pursuit, everything is resolved when the class finds the monster's actual baby and reuniting them together, and the monster releases Riiya.