When Sheriff Leo Wood is gunned down U.S. Marshal Lincoln is sent to Rustler's Gulch to find his killer. The marshal is convinced that it was the work of the corrupt businessman Clayton Finch. Unfortunately, his mission starts badly when his first arrest turns out to be a Pinkerton agent working undercover to bring down Clayton.

Lincoln releases the agent on the understanding that from now on they'll work together, but it soon becomes apparent that Lincoln has bigger problems to tackle. Clayton's activities have allowed a greater evil to flourish in Rustler's Gulch and it's one that'll require Lincoln to do something he never wanted to do and go undercover himself.