Phil Winslow goes out and gets rid of Marmaduke's dog house because a new one is on the way and goes inside to help the kids and Dottie with the school play the kids wrote. Phil is supposed to be a mean dog owner who wants to get rid of his dog and Marmaduke overhears him reading his part and thinks that they don't want him anymore so he leaves.
The family finds Marmaduke missing and they hop in the station wagon and go looking for him. Marmaduke winds up falling into a coal bin and looks like a black great dane. He sees the station wagon and tries to get their attention, but the Winslow family thinks that he's just another dog since he is black.
Marmaduke gets the coal dust knocked off of him when he runs into the animal control van and he runs into a pet store and hides in a dog house that says sold. The pet store delivers the house to the Winslow's house and when they get home, Marmaduke pops out much to everyone's delight.