Just as Halloween arrives, Chester Chipmunk claims to have solved the mystery of why a nearby woodland is known as the Forgotten Forest. His friends are sure that this is just another of his elaborate pranks. The thing is, his duck friend Billy Billington is going along with it and those two never agree! Reluctantly, Stanley Squirrel and his other friends agree to go along to learn the truth. Only what they find in the shadows under the leaves is far more weird and frightening than how the forest got its name!