Riders of the Purple Sage tells the story of Jane Withersteen and her battle to overcome persecution by members of her polygamous Mormon fundamentalist church. A leader of the church, Elder Tull, wants to marry her. Withersteen gets help from a number of friends, including Bern Venters and Lassiter, a famous gunman and killer of Mormons. Throughout most of the novel she struggles with her "blindness" to the evil nature of her church and its leaders, and tries to keep Venters and Lassiter from killing the adversaries who are slowly ruining her. When she adopts a child, Fay, she abandons her beliefs and discovers her true love. A second plot strand tells of Venters and his escape to the wilderness with a girl named Bess, "the rustler's girl," whom he has accidentally shot. Venters falls in love with the girl while caring for her. Together they escape to the East, while Lassiter, Fay, and Jane, pursued by both Mormons and rustlers, escape into a paradise-like valley and topple a giant rock to forever close off the only way in or out.