A posse discovers a trio of men they suspect of murder and cow theft and are split between handing them over to the law or lynching them on the spot.
Bolton has organized a feud between the Rork's and the O'Neil's. He has rustled cattle and killed a man putting the blame on Danny O'Neil. Tom Rork has found a bullet with markings on it that he hopes will clear Danny and bring in the real killer.
When his cattlemen abandon him for the gold fields, rancher Wil Andersen is forced to take on a collection of young boys as his cowboys in order to get his herd to market in time to avoid financial disaster. The boys learn to do a man's job under Andersen's tutelage, however, neither he nor the boys know that a gang of cattle thieves is stalking them.
Notorious shootist and womanizer Quirt Evans' horse collapses as he passes a Quaker family's home. Quirt has been wounded, and the kindly family takes him in to nurse him back to health against the advice of others. The handsome Evans quickly attracts the affections of their beautiful daughter, Penelope. He develops an affection for the family and their faith, but his troubled past follows him.
Bob Tyler has rustler trouble while driving a herd of cattle to the new owner, but he refuses to turn the herd over to Frank Kellogg. He has a run-in with Jean Polk, discovers she is the owner of the cattle, and is fired. With his friend, Barney McCool , Bob snoops around and discovers that Kellogg is behind the rustling.
When Matt Kilgore and his men frame and then hang an innocent man, Lige Saunders sends for his son Wild Bill Saunders who arrives to find his father shot by Matt's brother. When the brother is killed in his fight with Bill, Matt sends two fake Deputies to arrest Bill whom he then plans to hang. But Matt's sister, attracted to Bill, overhears the plan and rides for help.
Landis kills Tom Ross but fails to get his money. Now he is after the Ross ranch for the money he knows is there. When he tries to evict Ross with gambling IOU's, Bill drives him away. With the Ross cowhands out after his rustlers, he finds the money. But Bill is right on his trail.
Deputy Sheriff John Steele recruits bandit Sonora Joe to help him find out who's been bumping off all the local lawmen and rustling the cattle.
Hoppy goes undercover as a gambler from the East when Bar 20 cattle are stolen by unknown rustlers. Brennan/Talbot are twin brothers (one a casino owner, the other a rancher) and Hoppy believes they provide alibis for each other while one is out committing crimes. Hoppy gets a job in the casino to learn more but is exposed when a gambling gunslinger notices him.
U.S. Marshal Hopalong Cassidy is called when a town becomes overun with bad guys. Disguised as a member of a medicine show, Hoppy discovers that the ringleader is none other than sweet li'l ol' Ma Burton.
An evil gang is involved in both cattle rustling and the robbing of stagecoaches. Hoppy must stop them without help from the sheriff who turns out be a major outlaw himself.
A crusading newspaper editor recruits his old friend Hoppy to take the job of Marshall in a town rife with vice and murder directed at helpless miners.
On a cattle drive Hoppy, camp cook Windy, companion Lucky, and young Artie Peters encounter an eccentric professor. The professor professes to be searching for the evolutionary missing link, but in reality he is a cattle rustler who uses his dynamite to scatter the cattle in order capture some of them. Hoppy and Bar 20 guys ultimately capture the professor.
Hoppy's brother has been murdered and he is on the trail of the murderers. To get them he makes himself seem to be a wanted man.
Problems come in the form of one of Hopalong Cassidy's neighbors, but the matter is settled when Hoppy roots out the troublemaker.
The U.S. Army needs more horses for the Spanish-American War. Hoppy must turn his Bar 20 cowhands into Rough Riders to gather up the horses, and of course bad guys try to sabotage the operation.
Hoppy goes undercover as an outlaw (which permits him, for once, to drink and be mean to children) to track down a bunch of outlaws operating along the border. Loco, the head bad guy, deflects suspicion from himself by pretending to be a moron.
Hopalong Cassidy, boss of the Bar 20 ranch in Texas, rides down the Camino Real in the New Mexico cattle country near Alamogordo, in response to an urgent message from his lifelong sweetheart, Nora Blake, who is in serious trouble. Before he and his saddlemates, "Lucky" Jenkins and "Pappy", can reach her ranch, they are stopped by Clay Allison, a cattle-rustler who is in almost complete control of the district, and wants to extend his holdings by seizing Nora's cattle and driving her out. Seeing Cassidy as a menace to his plans, he has him arrested on a trumped-up charge. Cassidy and his pals shoot their way out of the trouble and reach Nora;s ranch where they learn that Allison's henchmen have murdered her foreman, Tom Dillon, and Allison has sent for a crew of outlaws on the Texas border.
Hoppy returns to find Johnny in trouble. Buck Peters has been shot by Porter who made it look like Johnny did it. When Johnny flees he runs into Linda. He takes a liking to her only to learn her father Shanghai is one of Porter's gang. Going after Shanghai, he gets captured by the gang and Porter now plans to kill him. But Hoppy is near by and Johnny will get unexpected help from Shanghai.
Hoppy clears Lucky on a charge of bank robbery and foils the plot of a crooked lawyer to rustle a herd of pedigree cattle and take over the valley.