The Swift Shadow, a dog trained to be a vicious killer, is captured by police after his master, Butch Kemp, commits a murder and flees. The dog is about to be put to death when Jim, the son of the murdered man, suggests that the criminal be tracked down with his own dog. The trail leads them to a ranch where Kemp attacks Jim and orders The Swift Shadow to finish him. The dog's gratitude for Jim's kindness prevents him from following Kemp's order, and in a frenzy of hate he kills his former master.