Yakari discovers a colony of beavers busy building their dam. There we find Thousand-mouths, the short-tempered building site boss; Wooden-Dam, the smiling old wise man; Wooden-Bed, the sleepyhead; Double-Tooth, the eternally inspired sculptor... and last but not least Little Linden Tree, a lively kid. While they are bathing, this infernal little beaver disappears. Yakari will find him exploring the underground waterways of the river. Linden Tree will, of course, receive his first smacking (Rough-Bark, his father, is so worried!) and Double-Tooth will finally be able to present his masterpiece to the amazed colony.