As the dusty town of Clearwater, Texas mourns the loss of Katie Elder, her four sons—John, a skilled marksman; Tom, an experienced gambler; Bud, an eager college freshman; and Matt, a modest hardware merchant—gather in their hometown in 1898 to pay tribute to their mother. This reunion is heavy with regrets as they come to terms with their shortcomings, realizing none have lived up to Katie Elder’s high hopes for them.
The townspeople continue to honor Katie's legacy, recalling her steadfast integrity, generous spirit despite her poverty, and unwavering love for her sons, even amidst their neglect. As the brothers debate how to properly honor her memory, a simple discussion about marble monuments escalates into a fight, which leads them to conclude that Bud should return to school.
Meanwhile, Morgan Hastings, a gunsmith turned businessman, claims the Elders’ expansive ranch and its vital water source, asserting he won it from their father, Bass Elder, in a high-stakes poker game. The mysterious death of Bass has gone unresolved for years, and the Elders suspect foul play. Anticipating trouble, Hastings employs a ruthless gunman named Curley to eliminate any opposition.
Hastings initially masks his ulterior motives, feigning concern and claiming he had offered compensation to Katie for her losses, which she purportedly declined. A local rancher named Striker entrusts the brothers with driving a herd of horses from Pecos to the mining towns of Colorado, a deal initiated by their mother on credit.
As Sheriff Billy Wilson confronts Hastings about his claims, the gunsmith coldly kills him and frames the Elders for the murder. On their return journey from Pecos, the brothers are intercepted by a posse; as Billy is gravely injured and unable to reveal the identity of his assassin, a lynch mob forms intending to hang the Elders. The judge takes action to protect them, ordering their transport to Laredo, away from the impending chaos in Clearwater.
As the transport convoys navigate perilous terrain, Deputy Sheriff Ben Latta remains committed to justice, though he harbors hostility toward the Elders. He finds himself clashing with Hastings, who signals an ambush using the deputized townsmen. Meanwhile, Curley’s sinister plans come to fruition as he secretly places dynamite beneath a bridge, triggering a devastating explosion that injures Matt and leaves John defensively killing Curley. Bud suffers severe injuries while Hastings, ever the manipulator, shoots Ben when he attempts to assist the Elders, before John and Tom bravely fend off the remaining attackers.
With night descending, Tom seizes a critical chance to kidnap Dave, Hastings’ weak-willed son, to expose his father’s misdeeds. However, Hastings outsmarts him, wounding Tom, and in a desperate act, kills his own son to ensure his secrets stay hidden. In Dave's final moments, he confesses his father's crimes, exonerating John.
Fueled by righteous anger, John arms himself and confronts Hastings at his gunsmith shop. A ferocious gunfight erupts, culminating in John’s fierce decision to ignite a barrel of gunpowder in the shop, reducing it to wreckage and marking Hastings’ end within.
