The Beavers are very worried: Linden Tree, Yakari's young and mischievous friend, has lost his appetite for... well, everything. And his people have no time to devote to him, as they must repair their precious dam, damaged by heavy rains. While the young Sioux attempts to dispel his friend's melancholy, Thousand-mouths suddenly realises he is several labourers short of a full work gang. Is something in the lake going after the hard-working beavers?