16-year-old Ben Mockridge has always wanted to be a cowboy and persuades Frank Culpepper to take him on a cattle drive. On the trail, Ben's romantic notions of the life of a cowhand are challenged as he learns about the exhausting, solitary, and violent aspects of the job.

In post-Civil War Texas, teenaged Ben Mockridge persuades cowboy Frank Culpepper to allow him to join his cattle drive to Fort Lewis, Colorado. Bidding his widowed mother farewell, Ben takes his cherished new pistol and happily assumes his position as the drive's "Little Mary," or cook's assistant. When Ben confides in the cook his dream of being a cowboy, the older man tells him that a cowboy is what someone does if they cannot do anything else. During the first few days of the drive, Ben struggles to help the cook and grows friendly with Pete, a cowhand who enjoys telling tall tales around the campfire. One night, two rustlers slip by the men on watch and start a stampede that kills one of Culpepper's men. After the men spend several hours rounding up the large herd, Pete reports to Culpepper that the rustlers have cordoned off two hundred head of cattle in a canyon nearby. Culpepper leads the men to the canyon, where the head rustler demands fifty cents per head to return the steers. Culpepper refuses and a gunfight breaks out in which all of the rustlers and three of the cowboys are killed. Although taken aback by the rush of violence, Ben quickly agrees to ride to the next town to contact Culpepper's acquaintance, Russell Caldwell, to hire four replacement hands. Upon reaching a river midway into the journey, Ben stops to bathe, only to have his horse and pistol stolen by a pair of elderly bandits. Arriving in the small town on foot, Ben locates Caldwell, who agrees to take hands Luke, Dixie Brick and Missoula with him to join Culpepper's drive. When the group comes across the bandits who stole Ben's horse, Ben is shocked when they kill the men without comment and seize their stolen goods. Upon reaching the herd, Caldwell demands a higher wage for himself and the others, but Culpepper refuses and Caldwell reluctantly backs down. The drive resumes and some days later, Ben pleads with Culpepper to allow him to help stand watch. Culpepper lets Ben watch over the horses, and the young man enthusiastically takes up his post. Late that night, however, Ben grows anxious in the darkness and is startled to come upon a stranger among the horses. Sensing Ben's inexperience, the man and his henchmen quickly disarm the boy, beat him up and steal several of the horses. Outraged by Ben's ineptness, Culpepper decides to put the youth on a Texas-bound train at the next town. After having Ben's injuries treated by the local dentist, the men stop at the small local saloon, where a shifty barman is impertinent to them. When Ben recognizes the rustlers at a card table, Culpepper confronts them. Noticing the barman reaching for a shotgun, Ben shoots him, provoking a fearsome shootout in which all of the bandits and gamblers are killed by the Culpepper crew. One lone survivor reveals the location of the horses, and the men move on while Ben remains in shock over having committed a murder. The drive resumes with Luke reflecting on whether a herd of cattle is worth all the difficulties and tribulations the men must face. At camp one afternoon, Ben spots Caldwell's gun near his bedroll and examines it, sending Caldwell into a fury. When Pete comes to Ben's aid and insults Caldwell, the latter challenges him. Perplexed by Caldwell's inflexible stance, Pete offers him an apology, but Caldwell continues to threaten him. When Pete turns to Culpepper to mitigate the situation, the leader refuses. Dismayed, Pete quits the drive and rides away as Ben looks on in confusion. Although Caldwell attempts to laugh off the confrontation, Culpepper angrily rebukes him for causing the loss of a good worker. The men and cattle press on and, after a blistering wind storm, are relieved to find fresh grass and water. Discovering a trampled fence, however, Culpepper realizes the men are on private property and goes in search of the land's owner. At a small town nearby Culpepper and the others learn at the local bar that all the land around them is owned by the wealthy Thorton Pierce. Pierce and his cronies find Culpepper at the bar and reject the cowman's offer to pay for the damaged fence and a trespassing fee. Demanding that Culpepper and the herd depart immediately, Pierce forces the men to surrender their guns and turn over their entire bankroll of two hundred dollars. Determined to depart as quickly as possible, Culpepper acquiesces and the men are stunned at having been deprived of their weapons. Back on the trail later that day, Luke reports grass and a river some miles ahead populated by welcoming settlers. Culpepper and the men discover the settlers are a religious sect and while Ben is fascinated by their belief in nonviolence, the others remain baffled. Soon after, however, Pierce arrives with his henchmen and declares the land is his property. When Culpepper demands to see a deed, Pierce indicates that his hired guns are his "deed." Giving them one hour to depart or face the consequences, Pierce has his men destroy the settlers' camp then rides away. Refusing to leave what he calls "God's land," the head of the settlers tells Culpepper he must protect them, but the cowman refuses. Dismayed, Ben announces that he will remain with the settlers. Having hidden his pistol from Pierce, Ben straps it on and stubbornly stays behind as the others ride away with the herd. Frustrated by their treatment at Pierce's hands and their disappointment in Culpepper, Caldwell, Luke, Dixie and Missoula demand the cook turn over his stash of rifles and return to Ben and the settlers. The men put up a furious resistance when Pierce and his men return, but all are slain as Ben watches in horror. Declaring the land now "soiled," the settlers' leader decides to move on, but Ben demands they help him bury his friends. Afterward, Ben throws his pistol on the ground and rides away.