Since Kassy managed to ride on a windmill, she has become the official guardian of the forest. And not only that - she is even a Florheart and has a special connection to the trees and bushes of the forest. Thanks to her abilities, she now leaves the gray squirrel Quirle behind in races - not to mention her friends Grace and Robinian. But soon it seems that the trees are listening to her less and less, and it becomes clear: The park no longer trusts the children as helpers! Even Camp Highwood, the school in the treetops, is under threat. Kassy must embark on the perilous journey to the heart of the forest and convince it that it can count on her.