In the dead of the night, a handful of brave men swear an oath that lawlessness must perish, and the Arizona Rangers, secret agents of the old West, are born. At their head rides Boone Yeager, determined to put an end to the band of outlaws that have overrun a small Western town. To accomplish his deed, Boone pretends to join the bandits, thus estranging his sweetheart, Letty Meade. Letty, believing that Boone has become a traitor, threatens to leave him if he does not end his association with the lawless element in their community, but Boone chooses not to explain things to her in order to keep his cover. As a result, Letty accepts the attentions of cavalry Lieutenant Bob Ives. Meanwhile, Boone is hauled to jail with the gang of outlaws for a crime they committed, and is stunned when he learns that Police Commissioner Teagle refuses to verify his claim that he is a government operative hired to infiltrate the outlaw gang. Deducing from Teagle's behavior that he is the leader of the outlaws, Boone makes a jailbreak and goes after him. After gathering enough evidence to put the outlaws behind bars, Boone rounds them up with the aid of the cavalry after a pitched stagecoach battle. His task accomplished, Boone reveals that he is actually the leader of the Rangers and wins back Letty's love.