In the mid-1800's, wagon trains functioned as a supply line, carrying provisions to the people of the frontier. One of these freight lines is operated by Zack Sibley, who took over the operation after his father was murdered by his partner, Carl Anderson. As Zack leads his wagons across the plains, Matt Gardner schemes to take over the freight lines and drive up prices. In league with Gardner to eliminate Zack is Gardner's son Coe and O'Follard, Zack's wagon master. Along the trail, Zack meets Helen Lee, who is coming West to marry Coe, and falls in love with her. Consequently, when Zack learns that a Comanche attack is imminent, he rides to Helen's stagecoach and offers her safe passage. When Coe, who has ridden to meet his fiancée, sees Zack embrace Helen, he swears revenge and organizes an ambush of Zack and the wagons. Out of loyalty to Coe, Helen refuses to join Zack's wagons, and soon afterward, the Indians attack the stage, sparing only Helen and Gardner. Zack offers the survivors refuge in his wagons, and they continue along the trail to Pecos. Meanwhile, in Pecos, Gardner's trading post has been price gouging, prompting an angry customer to accidentally set fire to the post, destroying the provisions. In desperation, one of the townsmen rides to Zack to urge him to hurry with the supplies to save the people of Pecos from starvation. This knowledge prompts O'Follard, who has a wife and child in town, to warn Zack about Coe's ambush and reveal that Gardner is really Carl Anderson, his father's murderer. Zack orders Gardner to ride to Coe and call off the raid, but Coe mistakes his father for Zack and shoots him and attacks the train. Zack and his men fight off the attack, but Coe escapes and rides to town, where the angry citizenry takes him prisoner. With the threat of the Gardners eliminated, Zack and Helen decide to marry and open a new trading post.
