Yakari discovers a colony of beavers building their dam. There he meets Thousand-Mouths, the short-tempered overseer; Dam-of-Wood, the smiling old wise man; Wooden-Bed, the sleepy-head; Double-Tooth, the eternally inspired sculptor; and last but not least Little Lime Tree, a lively kid. While they are bathing, this infernal little beaver disappears. Yakari eventually finds him in one of the river's underground waterways. Lime Tree is reprimanded by Rough-Bark, his father, and Double-Tooth finally unveils his masterpiece to the amazed colony.
