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.

Carter Filmore dirige la banque locale avec son fils, Ed, tandis que son second fils, Jim, s'occupe du ranch familial. Carter a investit de grosses sommes dans la construction de la ligne télégraphique, et, pour s'en sortir, envisage de vendre le ranch, ce à quoi Jim s'oppose formellement. Ed en profite pour persuader le vieil homme de modifier le testament en son unique faveur et de déshériter Jim. Mais Carter meurt avant de refaire le testament, et Ed falsifie le document.