The 19th Wife, By David Ebershoff

When Mitt Romney was running for the Republican nomination last year, he was asked: "If you were elected President, how many First Ladies could we expect?" Not missing a beat, he referred the questioner to the Latter-day Saints' website. Multiple marriage is a subject that mainstream Mormons wish would go away but, as David Ebershoff's new saga-length novel shows, its roots run as deep as the faith itself. Weaving together two stories, one historical, one contemporary, it throws new light on the rise and fall of American polygamy.

The dominant voice belongs to a real-life figure, Ann Eliza Young. The 19th wife of Mormon patriarch Brigham Young, she divorced her husband and went on to fight a campaign against polygamy and its woes. Her crusade resulted, in the 1890s, in the official rejection of plural marriage by the Mormon church. A fictionalised version of her popular memoirs, alongside letters and sermons, provide the period flavour of Ebershoff's tale.

Running in tandem is the story of construction worker Jordan Scott. Raised in a breakaway community of Saints, he was expelled as a teenager for holding his stepsister's hand. When he learns that his mother, also a 19th wife, has been arrested for the murder of his father, he suspects foul play and returns to Utah to clear her name.

Although very different in tone – one formal, one camp – both strands of the novel come together to form a fascinating overview of "Mormondom". The day-to-day realities of polygamy are brought home in the small domestic detail. Ann Eliza, the daughter of early converts, witnesses her mother's breakdown, following her father's conversion to "celestial marriage". First marrying the maid, he later succumbs to a frenzy of mid-life lust, wedding three women in three weeks. Back in the 21st century, Jordan recalls "laundry lines with 50 little shirts flapping in the wind", and the horror of coming face to face with his father's "marriage management notebook".

While respecting the power of religious conviction, Ebefshoff comes down hard on the self-righteous and self-serving. Mormonism may have gone from being America's most persecuted sect to its most robust, but for women and children at least, one of its more dubious doctrines has never proved heaven-sent.