In this animated adventure, chipmunk Alvin (Ross Bagdasarian) has werewolves on his mind. After being haunted by a creepy nightmare, he is convinced that his eerie next-door neighbor, Mr. Talbot (Maurice LaMarche), has a monstrous secret. As he and his brother Simon (also Bagdasarian) investigate, shy sibling Theodore (Janice Karman), who has been reluctantly cast in the school's production of "Dr. Jekyll and Mr. Hyde," finds his inner monster after being attacked by a strange dog.