Fanny relates the experiences of a 19th century missionary as she and her young husband proselytize throughout Europe in search of converts to the new Mormon faith. Her religious zeal is sorely tested upon receipt of news from America revealing that their religion has adopted the practice of polygamy as the means to exaltation. The couple is summoned to Utah only to find themselves firmly ensconced in Brigham Young's inner circle and called upon to practice plural marriage or risk a fall from family, friends, and faith.