In a simple act that changes her life forever, Cat-a sassy, young feral feline-leaps into a tree hole of a wise, old oak to escape from the 11-year-old cat wrangler Corner. From this moment forward, an unlikely gift of friendship develops between tree and cat. Sensing that the time is drawing near for the Dark Shadow's re-emergence and attack under the full lunar eclipse, Tree asks a favor of Cat. Tree explains that this will be his last-ditch effort for keeping an ancient promise to his father King Quercus. It is a promise that he and his siblings shamefully broke all those years ago. For her new friend's sake, Cat begrudgingly sets out on a quest to save the woods, the forgotten treechildren, Corner's dad, and the town itself from the Dark Shadow.