A young boxer Cal and his trainer Ray go to dive bars, where Ray bets on Cal to beat any challenger—man or woman, drunk or sober—foolish enough to take him on. There's no losing or forfeiting for Cal because Ray only goes home with winners.
The Good Boy opens with Ray and Cal at the Trash Bar, where Cal accepts a bet to fight a big lug named Quinny, only to discover that Quinny has the mental capacity of a five year old. Will Cal forfeit the fight and his relationship with Ray? Or will Cal inflict on Quinny the punishment needed to win the fight?