An outlaw (Charles King) murders a U.S. marshal and then flees south of the Mexican border. The Rough Riders are determined to bring him to justice, and they proceed by employing their preferred method: covert operations. Buck Roberts (Buck Jones) poses as a former criminal, Tim McCall (Tim McCoy) impersonates a cattle buyer and Sandy Hopkins (Raymond Hatton) assumes the role of a saloon handyman. They quietly gather information and use it to close in on the dastardly outlaw.