One day it starts to rain. A boy takes his favorite toy dog and they go outside to jump in muddy puddles. They get very dirty and decide to take a bath. During their bath a treasure map is discovered. The boy and his dog dive into the bathtub and go on an underwater adventure as they follow the instructions that are set in a series of rhymes. They help each other as they encounter new discoveries in the underwater world. In the end they find a delicious treasure chest hidden in a pirate ship.
