A new Bishop, Father Jean Marie Latour, is sent by Rome to spread Chrisitanity through new territory purchased in the Americas as part of the Gadsden Purchase. Father Latour takes with him his close friend, Father Jospeh Vaillant, to help with this cause. Latour is handsome, non-judgemental, amiable, keeps himself in check; Vaillant is his opposite, being not so pleasant of face but very very sociable and incredibly strong in faith.
There isn't much of a plot for this novel. It's more of a photo album or a series of episodes about the unexplored Western United States. The reader sees what the territory of New Mexico, Arizona and Mexico were like before trains, when the desert was both a beautiful and a harsh place. And, the reader learns about the people living there, from the French Fahters sent to Chrisitanize the Indians to the Mexican and Spanish settlers to the native Indians who are untrusting of white men and still hold to their gods. And the reader sees it all through the eyes of Father Latour so we get his wonder and awe at this strange, new world into which he's been sent to spread the word of God.