Bart (Bob Hoskins) is a vicious loan shark whose method of persuading men to pay him back involves Danny the Dog (Jet Li), a young man trained like a dog and left with the mentality of a child. Danny is a violently skilled fighter who stops at nothing to take down his targets, but only when a metal collar around his neck is removed by Bart. Once the collar is on, Danny is a harmless, withdrawn person, with very little knowledge of how to live as a Socialization human, and he is constantly bullied by Bart, whom Danny perceives as his master. One day, Danny meets Sam (Morgan Freeman), a kind blind pianist, at the antique warehouse while dealing with Bart's clients.