When a young boy (Liam Aiken) adopts a stray pup and names him Hubble, he thinks he's found the best friend he's always wanted. But he soon learns that dogs are aliens that have been sent to Earth to prepare for a canine invasion from outer space. Hubble (voiced by Matthew Broderick) finds that his fellow dogs are enjoying their lives as pets on Earth, and they must convince their leader that they're needed here -- or they'll be sent home forever!