After his business in Willcox, Texas, is robbed many times by a gang of masked bandits led by The Diablo Kid, banker Corthell wires the Texas Rangers in Pinecrest for help. Former cowboys Tim Holt and Chito Rafferty are assigned to the case and ride north for Willcox. Outside of town, Tim and Chito remove their Ranger badges to hide their identity and are then accosted by a group of gun-wielding men, who force them to ride to a nearby ranch. After Tim and Chito convince the ranch's suspicious owner, Gale Trevett, that they are out-of-work cowboys, Gale advises them to head west to find jobs. Tim and Chito continue to Willcox, however, and soon after, Corthell's bank is again robbed by The Diablo Kid's gang. As the outlaws are making their escape, Tim jumps The Diablo Kid, but is shot from behind by the town doctor, W. J. "Doc" Nichols. The Diablo Kid flees and is pursued by Marshal Tom Barlow, while Tim is taken to Doc for treatment. Aware only that his attacker fired a rifle at him, the slightly wounded Tim questions Doc about the assault. As Doc counsels Tim not to be too curious about The Diablo Kid, the gang, which is actually comprised of Gale, her uncle Henry and her cousins, count their stolen loot. Gale, who has been disguising herself as The Diablo Kid in order to rob the greedy, corrupt Corthell, divides the money up according to the specific needs of her neighboring ranchers. She then entrusts Artie, her young brother, to deliver the money, which she has placed in his lunch box, to Doc. While looking for Doc in Willcox, Artie runs into Chito and inquires about Tim's wound. Suspicious, Chito follows the boy into the town saloon, where he and one of Corthell's men both discover the contents of the lunch box and start to brawl. In the confusion, Artie escapes with the box and rushes to Doc's office. Corthell's man, meanwhile, shows the banker and Marshal Barlow a bill he snatched from Artie's box, and they both recognize it as part of the stolen cash. Barlow and Corthell intercept Doc and Artie as they are leaving town and, after finding the box and a note written by Gale, try to beat Doc into revealing her identity. Alerted by Artie, Tim and Chito stop the beating and expose themselves as Rangers. Reluctantly, Tim arrests Doc, but also fires Barlow and takes the money as evidence. Later, the Rangers question Artie about the money, but he maintains that he found it on the road. Acting on Tim's suggestion, Gale then starts to write Doc a testimonial, unaware that the Ranger actually wants a sample of her handwriting to compare with the note from the box. Before Tim can make the comparison, however, his pockets are picked, and the note is taken. Later, at the town jail, Tim again questions Doc about The Diablo Kid, but is told only that, like Robin Hood, the bandit robs from the rich and gives to the poor. As Doc is about to leave for Pinecrest with Chito, Tim and the money, Barlow, who is angry over his firing, poses as the masked bandit in order to steal back the cash for Corthell. At the same time, Gale dons her Diablo Kid mask, hoping to free Doc. Barlow and his men reach Doc first, however, and, after demanding the money, shoot and wound Doc before he identifies them as imposters. While pursuing Barlow, Tim meets up with Gale and finally exposes her as the bandit. Gale explains that she began her impersonation after Corthell and Barlow conspired to rob and kill her father as soon as he had finally saved up enough money to repay the banker's unreasonable loan demands. Doc then tells Tim and Chito that he recognized Barlow's horse during the ambush and sends them to the marshal's ranch. There, Tim and Chito engage in a gun battle with Barlow after he shoots Corthell in cold blood. The Trevett clan then comes to the Rangers' aid, and Tim arrests Barlow. Later, Chito and Doc head for Pinecrest, while Tim stays behind to obtain a deposition from a grateful Gale.