A young cowhand rebels against his rancher stepfather during a perilous cattle drive.

In 1851, Thomas Dunson and his friend, Groot Nadine, leave St. Louis and join a wagon train headed for California. When they reach the northern border of Texas, they decide to remain there and establish a cattle ranch. Fen, Tom's sweetheart, wants to stay with him, but he tells her that he will send for her later and gives her his mother's bracelet. Soon after Tom and Groot take their wagon and bull and head south to the Red River, they look back and see that the wagon train has been attacked and burned by Comanche Indians. That night, several Indians attack Tom and Groot's camp, and Tom is horrified to discover the bracelet he gave to Fen on the wrist of an Indian he killed in the struggle. The next day as Tom and Groot break camp, a young boy, Matthew Garth, who has escaped the wagon train massacre, wanders toward them with his cow. Tom and Groot take the dazed boy with them, cross the Red River and head farther south until, near the Rio Grande, Tom finds an area he likes. The land legally belongs, by land grant, to a Mexican, but after Tom kills one of the owner's gunmen and drives off another, he claims it for himself. Tom's bull and Matt's cow then become the beginning of a great herd sporting the Red River-D brand. Fifteen years later, the ranch boasts thousands of cattle, but Tom faces ruin unless he can move them from the impoverished, post-Civil War market. He decides to take ten thousand head a thousand miles to Missouri, where the railroads serve the North and East, and Matt, now grown to manhood and like a son to Tom, helps to plan the drive. Tom also agrees to take several head belonging to a neighboring rancher, and one of the neighbor's ranch hands, Cherry Valance, joins the drive. Both Cherry and Matt are expert gunmen and enjoy a friendly, if intense, rivalry. After a few days on the trail, the men reach the Brazos. Hills and rocks impede their progress and the cowboys become tired and unhappy. One night, when the cattle are restless, cowboy Bunk Kenneally, takes some sugar from Groot's chuckwagon and accidentally knocks over pots and pans, spooking the cattle and causing a stampede. Cowboy Dan Latimer is killed in the stampede, and although Bunk admits his mistake, he refuses to allow Tom to whip him and draws his gun. However, Matt shoots Bunk before he can shoot Tom. Forty days into the drive, the men are forced to endure heavy rains and short rations, as a grub wagon was lost in the stampede. Tom becomes very demanding and faces dissension among the cowboys. Some days later, a wounded wrangler from another drive rides into camp and explains that his group was attacked by a large gang of outlaws after they crossed the Red River. He also tells them about a trail blazed by an Indian trader, Jesse Chisholm, to a railroad terminus in Abilene, Kansas. When three of Tom's men state that they should be heading to Abilene instead of Missouri and threaten to quit, Tom kills them. More men desert with supplies and Tom sends Cherry after them. When the herd reaches the Red River, Tom decides to cross immediately despite the men's exhaustion. That night, Groot suggests to Tom, who has not been sleeping and has started drinking, that he tell the men that they did well, but he refuses. The next day, when Cherry returns with two of the deserters, Tom says he is going to hang them but Matt intervenes. As Tom goes to draw his gun on Matt, Cherry shoots him in the hand. Matt then assumes command of the drive, and they head to Abilene, leaving Tom behind. Tom swears that one day he will catch up with Matt and kill him. On the drive, Matt and the others encounter a wagon train being attacked by Apache Indians whom they help to drive off. Matt meets Tess Millay, one of the wagon train's settlers, and before he resumes the drive, they have fallen in love. Tom and some new men he has hired to pursue the train catch up with it, and when Tess tells Tom that she had wanted to go with Matt, Tom remembers leaving Fen. Tess then tries to persuade Tom not to kill his "son," and Tom offers her half of everything he owns if she will bear him a son. Tess agrees on condition he abandons his mission to kill Matt, but Tom declines. On 14 Aug 1865, Matt's team reaches Abilene and becomes the first cattle drive to cross over the Chisholm Trail. They receive a great welcome from the townspeople, and Melville, a representative of an Illinois trading company, makes Matt a very good offer for the herd and gives him a check payable to Tom. That night, Matt finds Tess waiting for him at his hotel. She warns him that Tom will be coming into town just after dawn to kill him. The next day, as Matt prepares to face Tom, Cherry challenges Tom, who shoots him but is injured by his return fire. Matt refuses to draw his gun against Tom, but when Tom attacks him with his fists, Matt fights back. Their brawl is interrupted by Tess, who fires a gun and angrily reminds them that they both love each other. After Tom tells Matt that he should marry Tess, he and Matt are finally reconciled. Tom then tells Matt that, as he had promised years before, he will create a new branding iron to include Matt's name, as he has earned it.