Aboard a passenger train enroute from Los Angeles to Chicago, a Christian movie actress named Mary meets an elderly woman and openly shares the struggles of her career and young faith. To her surprise, the lady next to her is 85-year-old Lettie Cowman, the author of the most beloved devotional of all time, Streams in the Desert. As the two women converse, Lettie reflects on the experiences and heartbreak that inspired her to write her famous book. As a girl growing up in small-town Iowa, Lettie falls in love with Charles Cowman, a telegraph operator at the Western Union office. A job promotion prompts them to move to a mining town in Colorado after marriage. However, Lettie soon becomes deathly ill, leading Charles to make a vow of service to the Lord that will change both of their lives forever.