Tom Fuller - a scrupulously honest fellow, a person of extraordinary physical strength, and owner of a savage horse, Rusty, that he alone was able to tame - is generally regarded as a half-wit. He has been summarily fired from every job he has ever had and even comes to regard himself as a failure. He makes one more try when he is hired on as a blacksmith's assistant by Boston Charlie. Finally here is a job that Tom can perform successfully, and his spirit soars.
Oliver Champion, who stops at the smithy to have his wagon horses newly shod, is impressed by Tom's ability. Champion also recognizes Tom as the son of the late Washington Fuller, a renowned gunfighter. Boston Charlie, far from being impressed by this revelation, is outraged and fires Tom, insisting that he leave at once. Champion takes this newfound opportunity to propose that Tom, who in addition to his physical strength is also an excellent shot, should become his bodyguard. Not having any alternative, Tom accepts the offer.
It is obviously a decision made in haste, as Tom soon learns that Champion is new to the West, that he is an escaped convict from a prison in the East, and that he has come all this way in pursuit of a master criminal, Henry Plank, the man actually responsible for the robbery for which Champion was imprisoned. Now Champion wants Tom to lead him through unfamiliar country to get his revenge.