Loan shark Bart (Bob Hoskins) took Danny (Jet Li) in when he was four years old, and since then he has trained Danny to be his loyal "wolf dog" by training wild animals. Bart's daily job is to lead his men to collect debts with Danny. If anyone dares to resist violently, Bart will release the collar on Danny's neck - that is the signal of attack, so that the latter can defeat the opponent with brutal and brutal moves. After each mission, Danny is sent back to the dark underground iron cage. During a fight, Danny met the blind tuner Sam (Morgan Freeman) by chance, and was deeply attracted by the piano and forgot Bart's mission. Furious, Bart sent Danny to the underground boxing ring that ended in death to earn more profits. On the way out of the boxing ring, Bart and his gang were ambushed by their enemies, but Danny survived and was taken in by Sam's family. In Sam's house, Danny experienced the missing family affection, gradually found his human side, and began to learn to play the piano. After Bart and his gang recovered from the disease, they took Danny back to the ring. However, Danny was no longer willing to kill, and he accidentally discovered the truth about his mother's murder. A decisive battle between Danny and Bart's gang was inevitable...