When they first encounter the antihuman rebels, who suggests they killed their owner? Duke. Who blames Max for bringing him back to his old house for no obvious reason? Duke. Who scares a lovely family back into a minivan? Duke. Who will be euthanized if he ends up in the pound again? Duke. Most importantly, who had no reservations about leaving Max for dead? Duke.

Duke, possibly accidentally, kills his owner and flees the scene, but not before taking a coin to remember him by. He ends up in the pound and the incidient makes the news. The new homeowners knew this and feared for their lives on seeing Duke, and the rawness of the emotion made Duke blame Max for pushing him to go back to the old house. Nobody will adopt Duke because of his infamy, except for one soft-hearted dog lover who gives him a home just before he is to be killed. As you might expect, that dog lover is Katie, Max's owner.