A terminally ill French secret service agent is hired by Hydra, a mysterious black ops organization set up by the government, to fight crime by any means necessary and receive experimental treatment in return. Also, his daughter hates him.

Raised as a slave, Danny is used to fighting for his survival. In fact, his "master," Bart, thinks of him as a pet and goes as far as leashing him with a collar so they can make money in fight clubs, where Danny is the main contender. When Bart's crew is in a car accident, Danny escapes and meets a blind, kindhearted piano tuner who takes him in and uses music to free the fighter's long-buried heart.