Posing as a cattle buyer, Hoppy crosses over into Oklahoma where the Jordan brother's and their outlaw gang operate outside the law. After receiving an unfriendly reception when he finds them, he, California, and Johnny rustle their cattle and drive across the river into Texas. He hopes they will cross over to retrieve their cattle and then he can arrest them.
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.
Hoppy and new sidekick California Carlson head to California to help out Lucky Jenkins.
Stephen Westcott and Ed Martin scheme to put Jane Travers' wagon line out of business. They want to use it take over all the wagon- train traffic going west. Hoppy, California and Lucky must make sure that doesn't happen.
Stagecoach robbers take the money Hoppy was going to use to buy cattle so Hoppy, California and Lin go after them.
Before he was killed by Mark Foster's men, Bud Lawton willed part ownership in his ranch to Hoppy and his two pals. When the three arrive they find a fake posing as Lawton. When they expose the imposter, Foster gets the Sheriff to jail them for Lawton's murder.
Easterner Madeline Hammond buys a ranch not knowing Hayworth is using it to smuggle ammunition across the border. When trouble starts, she brings back Gene Stewart ex-foreman who left the country after fighting with the Sheriff.
Bat Masterson, who after failing to secure a job as a newspaper reporter becomes marshal of Dodge City. Preferring socializing to peacekeeping, Masterson falls in love with Dora Hand, the obligatory golden-hearted chorus girl whose concern for the welfare of her fellow citizens at time reaches Madonna-like dimensions. When Dora is shot down cattle baron King Kennedy, Masterson begins taking his job seriously. After taking care of Kennedy, Masterson determines to enshrine the memory of Dora, whose efforts to clean up Dodge City were largely ignored by the "decent" townsfolk.
A beautiful heiress is an excellent poker player. Her comfortable life changes when her father and his fortune die during market crash of the 1800's.
The local school is causing Hoppy problems. First Bar 20 cattle are stolen when Hoppy investigates a problem there. Then the new teacher arrives and disrupts the routine of the Bar 20 hands. Later with the Bar 20 hands at graduation, the rustlers are poised to strike again. But there is dissension among them and this will lead to the break that Hoppy needs.
Buck Colins heads a group of local ranchers who are trying to prevent the railroad from completing its line through their property. Till now they have been able to charge tolls on herds passing through. Hoppy goes undercover to expose them.
Julie's husband has been murdered and land agents want her to sign away her property rights. Hoppy warns against this but she does so anyway. It looks as though she will be unable to deliver the timber called for in her agreement. Hoppy has to make the lumber deal happened and solve the murder.
Burton is after Clark's ranch. He gets the banker to refuse to renew Clark's note and then sends his men to rustle his cattle. Hoppy is Clark's new foreman and is on to Burton's scheme. But just as he learns of the rustling and is about to go after the gang, the Sheriff arrives and arrests him for hiding Johnny who has been accused of robbery.
Originally written as a stage vehicle for corpulent character actor Macklyn Arbuckle, Ernest Day's The Roundup was first filmed in 1920 with Fatty Arbuckle (no relation) in the lead. By the time the film was remade in 1941, Arbuckle's character, a roly-poly frontier sheriff named Slim (!), was refashioned as a supporting role, with Jack Benny's radio announcer Don Wilson essaying the part. The plot, however, remained fairly intact: Upon hearing that her fiance Greg (Preston Foster) has been killed, Janet (Patricia Morison) agrees to marry rancher Steve (Richard Dix) on the rebound. On the day of the wedding, who should show up but Greg, determined to raise as much Hell as humanly possible
When Ranger Hoppy's falsely accused young ranger friend is killed while supposedly trying to escape from jail, Hoppy is blamed and drummed out of the Texas Rangers.
As rustled cattle have mysteriously disappeared, Johnny sends for his friend Hoppy, Hoppy arrives and immediately suspects Dan Slack. Realizing his telegram about Slack was intercepted, he locks up the operator Lafe knowing he can escape. Tailing Lafe he finds a secret entrance to a mine and inside finds the missing cattle. But Slack's men also find him just as the cattle are stampeded through the mine shaft.
Hoppy, California and Johnny partner up with brother and sister ranch owners, two of several who are having their access to water blocked by a dam owned by a greedy merchant in town, who is intent on driving them out and taking their land for himself.
A railroad man and the owner of a freight line battle for control of a crucial mountain pass.
Cowboy Ross McEwen arrives in town. He asks the banker for a loan of $2000. When the banker asks about securing a loan that large, McEwen shows him his six-gun collateral. The banker hands over the money in exchange for an I.O.U., signed "Jefferson Davis". McEwen rides out of town and catches a train, but not before being bitten by a rattler. On the train, a nurse, Miss Hollister, tends to his wound. A posse searches the train, but McEwen manages to escape notice. However a mysterious Mexican has taken note of the cowboy, and that loudmouthed brat is still nosing around. Who will be the first to claim the reward for the robber's capture?
Caldwell and Nixon have their men rob the stage and then critcize the Sheriff for not catching the robbers. With her father the Sheriff under pressure, Mary sends for Hoppy who finds the stolen money and sets a trap to bring in the entire gang.
