Former Texas Ranger Lassiter leaves Texas and travels to Arizona sage country pursuing a group of Mormons who abducted his married sister. He arrives at the Withersteen ranch near the Utah border, where his sister was last seen. He meets the Withersteens and their beautiful daughter, Jane. Lassiter rescues her rider, Venters, from torture at the hands of a villain named Tull. Soon, Lassiter falls in love with Jane, but when she learns about his mission, she is reluctant to help him, fearing more violence will come to the region. Her feelings for him change, however, when she sees the hardened gunfighter befriend her ward, a young orphan girl named Fay Larkin. While Venters is out searching for the rustlers who have been raiding the Withersteens' ranch and stealing their cattle, he wounds and captures the rustlers' masked leader, who turns out to be a beautiful young woman. Rather than turning her over to the law, Venters brings her to a secluded valley, where the two fall in love. Meanwhile, Lassiter learns that his sister is dead, and that the man who abducted her, Dyer, is also responsible for much of the trouble faced by Jane and her family. Lassiter tracks the villain and raids a Mormon meeting, killing Dyer. The angry Mormons then pursue Lassiter, Jane, and Fay to the secluded valley where they meet Venters and the repentant cattle thief, whom Lassiter recognizes as his dead sister's daughter, Millie. Venters and the girl escape the Mormons, but Lassiter, in rolling a huge boulder down on his pursuers, blocks the only exit to the valley, trapping himself, Jane, and Fay inside the valley forever.
Riders of the Purple Sage features uncredited bit parts by future silent film stars Buck Jones and Jack Nelson.
Reception
Riders of the Purple Sage received mixed reviews upon its theatrical release in 1918. The reviewer for Motion Picture News wrote: The reviewer for Variety called the film a "not-too-absorbing adaptation of the novel", noting that the film "does not rise above the level of the average Western photoplay of this type and there is no special distinction in direction or photography." In her review for Allmovie, Janiss Garza wrote that despite the "rousing climax", the film was "not one of the better adaptations of the Zane Grey novel." Like many American films of the time, Riders of the Purple Sage was subject to restrictions and cuts by city and state film censorship boards. For example, the Chicago Board of Censors required a cut, in Reel 3, of the man falling after Lassiter shoots, Reel 6, the intertitle "He made me — I can't tell you — I can't —", the shooting of Oldring, and, Reel 7, last shooting scene in which a Mormon is killed.
