The hero, Texas Ranger Larry Whalen (Charles Starrett), is on the trail of a mysterious outlaw leader.

Roy is an oil prospector. His efforts to get drilling rights on an old Spanish land grant are countered by gamblers from an off-shore gambling boat determined to control the land (and oil) themselves.

Thelma and Patsy get jobs at a radio station.

Steve Beaumont, an operative for the Cattleman's Protective Association, is assigned the difficult task of breaking up a murderous gang of rustlers led by Ed Brock and Strang. He takes Sheriff Webb, Judge Baxter, and rancher Ann Houston into his confidence, and works his way into the rustler stronghold and confidence by "turning rustler" himself.

The Kinkaids and the Harpers both run stage lines and are friendly competitors. Appleby is after the stage line and convinces the two owners to build a spur line to the same town. Then he has both projects sabotaged pitting the friends against each other and running them out of money.

After a handful of non-formula westerns, Charles Starrett returned to the mixture as before in Thundering Frontier. Starrett plays Jim Fillmore, kind to old ladies, small animals and heroine Norma Belknap (Iris Meredith). In contrast, the villains are kind to no one, least of all struggling building contractor Square Deal Scottie (Alex Callam), whose projects are continually targeted for demolition and his payroll is forever being stolen at gunpoint. A good 25 percent of the film's running time is given over to Bob Nolan and the Sons of the Pioneers, whose C&W croonings are pleasant but a bit much. One of the film's few surprises is that Starrett's perennial screen sparring partner Dick Curtis isn't one of the bad guys.

The Pony Express is finished as the Post Office plans to award the mail contract to a stage line. Bill and his father put in a bid for the mail, however there are three bids close together. The officials will run a race to pick the winner, and the Banton Brothers sabotage Bill's stage. Mary still believes in Bill until they try to get rid of him by holding up the regular stage with his well-known horse. Bill needs proof to clear himself and expose the bad guys.

Frank Sr. sells his supplies to Hook, but then Hook has the Bannion Boys bushwhack his wagon to get the money back. Frank is murdered, but Junior gets away. He comes back 10 years later to settle the score as the Singing Cowboy. He finds that Hook is still doing his dirty deeds on the unsuspecting people. Along the way, Frank meets the lovely Jen, who came out in the same wagon train 10 years before.

Cowboy Jeff Larabee returns from the east and meets Doris Halloway, a young girl, that he regards as a vagabond, till he learns that she's the owner of the farm where he works. He tries to win her heart, but without success, until she is endangered by gangsters

A singing entomologist (Roy Rogers) acts meek to help a juggling sheriff (George "Gabby" Hayes) solve ranch raids.