Ten years after the events of Riders of the Purple Sage, John Shefford, a disillusioned preacher from Illinois travels to Arizona and takes refuge in a village controlled by polygamist Mormons hiding from the federal government. It's there Shefford learns the story of Fay Larkin: years ago, the infant Fay, along with Jane Withersteen and a gunslinger known as Lassiter, were trapped in Surprise Valley. Intrigued, Shefford decides to track Fay down. Originally published under the title The Rainbow Trail in 1915, it was re-edited and re-released in recent years as The Desert Crucible.