Texas Rangers Hopalong Cassidy, California Carlson and Jimmy Rogers rescue their friend, rancher Tim Mason, from a saloon, when Tim loses all his money in a card game to the outlaw "Gunner" Madigan. Tim's sister Sue then surprises them with a celebration because Tim has been appointed a Texas Ranger through Hoppy's influence. Tim goes to the bank and, as his loan is due that day, admits to bank president Simon Crandall that he has squandered his loan on gambling instead of replenishing his cattle. Crandall earns Tim's trust by promising his help so that Tim's fears of losing the ranch will be dissuaded. Crandall, however, is the mastermind behind a smuggling operation and intends to blackmail Tim into allowing his wagons to cross the border on Tim's land. After Tim is sworn in as a Texas Ranger, Madigan shows him that he now holds the note against his ranch, and demands that Tim allow his wagons to cross the land. Tim refuses to allow the wagons to pass, and Madigan's cohort, Nick Drago, knocks him unconscious. Just then, Hoppy, California and Jimmy happen to ride by and after exchanging gunfire with the outlaws, capture the wagon. The dying driver says that he thought the Rangers were paid off. Tim is arrested by Texas Ranger head Captain Jennings after he refuses to defend himself. Hoppy assures Sue that Tim will never see a trial, but Tim refuses to speak to him. When Hoppy leaves the jail, deputy sheriff Martin, who is in cahoots with Crandall, murders Tim, and frames Hoppy for assisting Tim's supposed jailbreak attempt. Circumstantial evidence works against Hoppy and after he angrily strikes Jennings, he is dismissed from the Rangers. A disgruntled Hoppy joins up with Madigan, and for his initiation steals back the supply wagon. Hoppy is captured, and reports his findings to Jennings, for whom he is actually working undercover. Jennings then releases him, but to maintain his cover, makes it look as if Hoppy has escaped. Crandall, in the meantime, takes over Sue's ranch operations with her cooperation, ostensibly so that she can slowly pay off Tim's loan. Unknown to Sue, Crandall uses her barn to store smuggled goods. When Sue's ranch hand Sourdough reports that their own supplies are being stolen, she and Sourdough discover the boxes of smuggled weapons and are captured by Madigan's gang. Fearing further discovery, Madigan plans his escape. Hoppy, meanwhile, knocks out Drago and releases Sue after she tells him about Crandall's involvement. Madigan confronts Crandall at the bank and Crandall murders him. The Rangers then shoot Drago to keep him from murdering Hoppy, and Crandall is arrested. Hoppy is promoted to captain and given charge of his own Rangers outpost, after which he, California and Jimmy bid farewell to Sue.