After the Civil War, former slave and Union Army sergeant Buck becomes a wagon master and leads freed slaves to the West in search of a better life. The homesteaders are plagued by mercenary soldiers known as night riders, hired by Southern plantation owners, who destroy their supplies in order to force them to return to work in the South. After terrorizing one group, the night riders’ leader, former Confederate soldier Beau Deshay, plans to ambush Buck at the farm belonging to his woman, Ruth. Buck escapes, however, and after spotting a solitary campfire with a horse tethered nearby, begins to swap his exhausted horse for the fresh horse. However, when the horse's owner, a former slave and glib con man who wears clerical garb, spouts biblical verses and calls himself Preacher, protests, Buck levels his gun at him and rides off. The disgruntled Preacher proceeds to a small boomtown and there meets a young black child named Little Toby, who tells him that his people have planted a crop for a local farmer and are about to head West. Preacher is then accosted by Deshay, who recognizes Buck’s horse and demands to know Buck’s location. After Preacher, who introduces himself as Reverend Willis Oakes Rutherford of the High and Low Order of the Holiness Persuasion Church, convinces him that he does not know Buck's whereabouts, Deshay offers him a $500 reward for Buck, dead or alive, and tells him that the night riders reside in the town of Copper Springs. Preacher goes with Toby to meet his family and discovers that they are from St. Anne’s Parish in Louisiana. Much to Preacher’s surprise, Buck is their wagon master, and upon seeing him, Preacher knocks the scout down with a mighty punch. Buck agrees to trade horses again but, mistrusting Preacher, orders him not to accompany the group. The pioneers are loaded down with supplies and are carrying almost $2,000, which is hidden in a belt worn by a young woman. Preacher, having seen the money, is determined to go along, but the next day, Buck forces him to leave. Buck then gives the group’s leader, Kingston, directions to the next waterhole and promises to rejoin them soon. Preacher trails Buck and catches up to him, but is terrified when Indian warriors appear, although Buck calmly dismounts and prepares to talk to the Indians. Through Sinsie, the chief’s wife and translator, Buck requests safe passage for the settlers and the right to hunt buffalo. The chief and Buck agree on a price, although the chief allows them only five days to cross. That night, while Preacher and Buck rest at their campsite, the settlers are attacked by Deshay and his men. With their money stolen, supplies destroyed and several people murdered, the homesteaders are heartbroken, but old Cudjo, one of the homesteaders, throws his fortune-telling bones and declares that a lush valley awaits them. Buck and Preacher are dismayed upon seeing the devastation, and when the group insists on continuing, Buck assures them that they have safe passage. Preacher is especially distraught by Toby’s death and informs Buck that Deshay’s gang is at Copper Springs. Determined to retrieve the settlers’ money, Buck and Preacher head for the town while the wagon train moves on. In Copper Springs, Sheriff Jeff Harley warns Deshay that it is illegal to assault the pioneers, but Deshay insists that as “bona fide labor recruiters,” they have a right to “preserve” the pre-war way of life. At night, Deshay and seven of his men are relaxing at Madam Esther’s bordello when Preacher bursts in to distract them. Preacher makes the men laugh as he declaims against fornication, and when their guard is down, Buck enters and a gunfight ensues. Buck and Preacher, who keeps a large pistol hidden in his Bible, kill their enemies, although two of the gang members, who are in the saloon, escape. Floyd, Deshay’s nephew, and the other rider join the sheriff’s posse in pursuit of Buck and Preacher, but the two black men elude them. While they rest, Buck is disgusted to discover that the mercenaries had already squandered most of the settlers’ money. Buck and Preacher then ride to Ruth’s cabin, where she declares that she wants to move to Canada with Buck to raise a family in a land free from any “shadow of slavery.” Ruth asserts that the idealistic Buck has done as much as one man can, but Buck maintains that he gave his word to the homesteaders. Reluctantly, Ruth accompanies Buck and Preacher, with the trio leaving just ahead of the pursuing posse. Later, at camp, Buck confesses to Ruth that he feels beaten by the night riders and their violence, even though he had survived both slavery and fighting in the war. Preacher then reveals that he got the “funny Bible” that hides his pistol after killing the white preacher who owned and abused him and his mother. As Buck ponders how to replenish the settlers’ money, Preacher suggests robbing the bank at Copper Springs, because all the men are out searching for them. With Ruth’s help, Buck and Preacher succeed in stealing the money and are about to ride away quietly when one of their captives raises the alarm. The posse, which had returned during the robbery, chases the fleeing trio but is stopped when the fugitives ride through a line of Indians, who close their ranks against the whites. Although Floyd wants to fight through the Indians, Harley warns that they will be slaughtered if they pursue Buck. The trio is taken to the chief, who states that although they are guaranteed safe passage, the Indians will not fight for them, nor sell them any of their own much-needed firearms. Meanwhile, the posse has found the St. Anne Parish wagon train, upon which Floyd and Harley spy from a nearby ridge. Floyd wants to attack the settlers but Harley rebukes him, after which Floyd kills the sheriff and tells the posse that Harley approved the raid. As the posse rides down the hillside, they are spotted by Buck, who gives the money to Ruth, then rides with Preacher in the opposite direction to draw off their pursuers. Buck and Preacher allow themselves to be chased up into a rocky hillside and a prolonged shootout begins, during which the pair kills several posse members and are wounded themselves. Just as they are about to be gunned down, the watching chief sends his warriors to help them. The surviving posse members are either killed or frightened off, and Buck and Preacher are saved by Ruth and Kingston. Later, the settlers survey the beautiful valley foretold by Cudjo then bid farewell to Buck, Ruth and Preacher, who ride north toward their own destiny.