The Lone Defender

As they return from their secret mine in the desert, prospectors Juan Valdez and Burke are ambushed. Burke escapes but Valdez is shot and killed. A notorious bandit, The Cactus Kid, is suspected of the crime. Ramon, actually a Justice Department Agent named Marco Roberti, a mysterious figure, overhears a conversation between two townsmen, Halkey and Jenkins in which they discuss their failure to get the location map of the mine from Valdez. Rinty, Valdez's dog,recognizes Jenkins as his master's killer and attacks him. Halkey, actually "The Cactus Kid", decides to capture Rinty as he thinks the dog can lead him to the mine.