With his parents (MOLLY SHANNON & (KEVIN NEALON) perpetually buying, renovating and then selling house after house, young Owen (LIAM AIKEN) has little time to make lasting friends. Having run a successful dog-walking business for the neighbors, he's raised enough money to get his own dog that he hopes truly will be man's, or at least his best friend.
He goes to the pound, picks up a mutt with a bad attitude, and names him Hubble (voice of MATTHEW BRODERICK). The pooch doesn't seem to want to do what Owen wants and the boy soon learns why. It turns out that Hubble is really Candid 3942 who's been sent by The Greater Dane (voice of VANESSA REDGRAVE) of the planet Sirious to discover why after thousands of years, dogs still have not taken over the planet.
To his shock, Hubble discovers that dogs are the human's pets. To make matters worse, Owen is accidentally endowed with the ability to understand him and the rest of the dogs. They include the pampered poodle Barbara Ann (voice of DELTA BURKE), cool boxer Wilson (voice of DONALD FAISON), nervous Italian greyhound Nellie (voice of BRITTANY MURPHY) and gassy Bernese mountain dog Shep (voice of CARL REINER).
Things get worse when Hubble learns that the Greater Dane is headed for Earth to do her own inspection. Knowing that if things don't look right all dogs on Earth will be recalled to Sirius, he and Owen then set out to whip the other dogs into shape so that they can pass muster.