Max is dog living a life of relative bliss in a New York City apartment who gets all of the love and attention he needs when his owner Katie's home, but now finds himself having to compete when bleeding-heart Katie brings home a shelter pooch in the form of the big, dopey, shaggy-haired Duke, who steals that attention, as well as a good deal of the food and pet bed. Squabbles result on who is going to be 'alpha dog' before both find themselves having to ally when they end up out in the streets of the city without an easy means of returning home in one piece. Out to the rescue are a few of their pet animal friends, who've made it their mission to bring Max back, and they have to do it fast, as the mutts have made enemies with a psychopathic bunny rabbit named Snowball, the gang leader of a rag-tag group of vicious street rejects who hate pampered, domesticated pets and their human owners.