In a world of talking animals, there is one burning question: Did humans ever exist? Thelonious Chipmunk believes he has proof that they did: a postcard showing a building made of concrete and glass. But his sister thinks the postcard's just a dumb piece of paper, and that humans are only make-believe. Then one day a flash flood carries Thelonious away. When he comes to, he's in a strange world that looks something like his postcard, but not quite...