A fiery half-breed comes between a rancher's good and evil sons.

Before Scott Chavez is hanged for the murder of his Indian wife and her lover, he makes his beautiful but unrefined daughter Pearl promise that she will grow up to be a lady like Laura Belle McCanles, his former sweetheart. Laura Belle offers Pearl a home on Spanish Bit, the Texas cattle ranch where she lives with her husband, "Senator" McCanles, and her two sons, Jesse and Lewt. Although McCanles, who is confined to a wheelchair, is hostile toward Pearl, her beauty immediately attracts the attentions of both Jesse and Lewt. One night, when Pearl goes to bed, Lewt forces his way into her room and kisses her. Although Pearl loves the kindhearted Jesse, she is physically drawn to the wild, handsome Lewt and, despite the prayers of preacher Jubal Crabbe, who is known as "the sinkiller," cannot resist him. When a railroad company wins the legal right to build tracks through the million-acre McCanles ranch, McCanles gathers all the ranch hands to defend the border against the railroad crew. In order to prevent bloodshed, Jesse, a lawyer, takes the side of the railroad and is banned from the ranch by his father. When Lewt returns from El Paso, he takes advantage of the deserted house to seduce Pearl. Jesse finds them together and confesses that although he loves her, he will never forget what he has seen. Pearl now pushes Lewt to marry her, but when he makes it clear that he has no intention of being tied down, she quickly becomes engaged to Sam Pierce, a much older cowhand. Lewt is overcome with jealousy and kills Sam. After a reward is posted for Lewt's capture, McCanles sends Lewt, his favorite son, to Mexico. Before Lewt goes into hiding, he derails a train carrying explosives that is headed for Spanish Bit. He then stops at the ranch to say goodbye to Pearl, who begs to come with him. Lewt roughly rejects her, and Pearl is left alone with McCanles and the dying Laura Belle. Faced with losing his wife so soon after losing both his sons, McCanles tells Laura Belle that although he has always blamed her for the injury he received while chasing her when he thought she was running away to join Chavez, he realizes now it was his own jealousy that was responsible. He admits that he loved her then and still loves her. After begging her husband's forgiveness, Laura Belle dies. Unaware that his mother is dead, Jesse returns to the ranch to see her. Pearl has suffered a breakdown since Laura Belle's death, and Jesse, who is now engaged to Helen Langford, the daughter of a railroad man, takes her away from the ranch. Lewt comes after Pearl and, when Jesse refuses to let him near her, shoots his brother. Jesse survives and is reconciled with his father, but Pearl understands that Lewt will eventually kill Jesse. In order to prevent that, she agrees to meet Lewt at Squaw's Head Rock, intending to kill him. Pearl's first shot wounds Lewt, who not quite dead, returns her fire, wounding her. The two dying lovers crawl toward each other and die together under the blazing sun.