Express agent Randy Bowers rides to Ed Rogers' desert "halfway house" and discovers the proprietor's slain body and a "wanted" poster inscribed with a threatening message from outlaw Marvin Black. Before he can defend himself, Randy is arrested by the sheriff and is escorted by the posse to the town jail. After the saloon clears, Ed's niece, Sally Rogers, emerges from a hiding place and checks her uncle's strong box, which is buried under the floorboards. Confident that the money is safe, Sally rides to town and agrees to view the suspect in his cell. While the sheriff is away, Randy shows Sally a letter from the Adams Express Company in which he is identified as an express agent who had been sent to protect Ed. Convinced of Randy's innocence, Sally slips him the cell key and leaves. Sally then is approached by storeowner Matt the Mute, in reality Marvin Black in an elaborate hunchback disguise, who offers to buy the saloon as a "goodwill" gesture. After Sally turns down Black's offer, Randy executes a perfect escape and rides to Sally's saloon. While Randy explains to Sally his preference to work alone, the sheriff and his posse descend on the house. During his second escape, Randy stumbles on Black's cave hideout, where he is discovered by Spike, one of Black's henchmen. At Black's insistence, Randy is initiated into the gang and is shown the mines of dynamite that protect the hideout. Determined to steal not only her land but her money as well, Black kidnaps Sally and, when she refuses to reveal the whereabouts of her money, locks her in a closet. During the night, however, Sally slips Randy the strong box key and tells him where the box is hidden. The next morning, Randy substitutes the strong box cash for a load of dynamite, then, having deduced that Black and Matt the Mute are the same person, leads the sheriff's posse to the hideout. During the ensuing shootout, Randy chases Black to the saloon, where the outlaw prepares to open the box. As Sally and the sheriff's posse arrive, an explosion destroys the saloon. Vindicated by the sheriff, Randy rides off with Sally.