Owen Baker is the 12-year-old dog walker of the neighborhood who has taken up the job to earn the responsibility of owning his own dog. One day, he adopts a Border Terrier which he names Hubble. He is soon shocked to find his dog can talk, and the dog whose real name is Canid 3942 tells him about how dogs were sent to Earth thousands of years ago from the Dog Star Sirius 7 in order to colonize and take over the planet. After Canid learns from the rest of the Earth's dogs that they are instead being kept as pets, he forewarns that the Greater Dane of Sirius 7 will return to Earth today to judge the dogs' takeover, and if they have failed, he will recall them to the star. Owen and his dog now have a day to encourage the Greater Dane that dogs and humans live very well together and that they should remain on the earth.