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.
William BoydHopalong Cassidy
Russell HaydenLucky Jenkins
Britt WoodSpeedy MacGinnis
Pedro de CordobaPadre Jose
Willard RobertsonBuck Collins
Matt MooreMarlow
Betty MoranEllen Marlow
Kenneth HarlanChas. Higgins
Francis McDonaldMorgan
Eddie DeanPete
Hoppy and his pals arrive in a remote town to investigate the counterfeiting of both U.S. and Mexican money; his only clues are the name "Mordigan" and a drawing of a comet. He quickly finds out that Mordigan is the town "boss"; but what or who is "the comet", and why are Mordigan and his henchmen intent on persecuting a young woman, her drunken brother, and her deathly ill sister-in-law who've also just arrived in town?
Hoppy, California and Johnny come to the ranch of a friend and his daughter, disguised as dude detectives from the east, to investigate the disappearances, without a trace, of several herds of cattle.
Hoppy, Johnny and California go to Arabia to buy some horses. There they get involved with a sheik and a harem and a kidnapping plot.
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.
Stagecoach robbers take the money Hoppy was going to use to buy cattle so Hoppy, California and Lin go after them.
When the outlaw El Toro saves Hoppy's life, Hoppy agrees to find his missing grandson.
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.
Hoppy's friend Dennis owns a rich gold mine. Frazier who owns the adjoining mine and wants the Dennis mine, has Dennis killed. Hoppy steps in to take over running the Dennis mine and learns Frazier's men sneak into and work the Dennis mine at night. Hoppy captures one of Frazier's men only to be captured in return by Frazier and left to die in a burning building.
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.
Escaped criminal "The Fox" hates Hoppy and a Rurales colonel for imprisoning him and lures Cassidy to Mexico in order to exact his vengeance.
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.
Hoppy and Lucky are headed to South America to deliver a heard of cattle. Bay guy Ralph Merritt gets in their way. For a while.
Hoppy goes to town to help Marshal Windy with some rustlers and winds up helping the widow Joyce when confidence men try to take her herd. King's Men songs include: "Hi Thar Stranger" and "Lazy Rolls the Rio Grande."
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.