Not only does it give historical consideration to this practice, but it also looks at its existence in modern day break-away LDS groups/sects (or whatever word you would like to insert here).
Ebershoff achieves this with two distinct story lines.
The first is the historical story line of Anne Eliza Young, one of the wives (the 19th in fact) of the Prophet Brigham Young. It is set in the late 19th century and although it is a fictional story, it is based on the real Anne Eliza Young, who was actually married to the Prophet and who became famous when she broke from the LDS and began a campaign to end polygamy.
There are parallels between this historical storyline and the modern day story of Jordan Scott, a man who grew up in a breakaway group of the LDS which still practised polygamy. Although polygamy is now illegal, the story is also based on real break away groups of the LDS that are based somewhere in America (sorry, I'm an Aussie, can't remember where, maybe Utah?) and who still practice polygamy. Jordan becomes involved with the community again when his mother, the 19th wife of his father, is accused of his father's murder.
Through the eyes of Anne Eliza we see how polygamy affected the women and children at the time when the LDS was in its early days, and through Jordan's eyes we see the impact it has had for current practitioners of this religion (both the breakaway groups and the main body of the Church).
Although fictional, The 19th Wife is clearly well researched, and it is this sense of authenticity that really peaked my interest.
Ebershoff tells Anne Eliza's story through her own words, but also through a series of fictional documents, including memoirs of her family members, letters and newspaper articles. Whilst this was a novel approach to presenting the story of Anne Eliza, at times it meant that her story wasn't as cohesive as it could have been, both as a standalone story, and how it sat in the context of the entire book. The book was at times frustrating because it moved frequently between the two protagonists, as well as the additional mediums used to tell Anne Eliza's story. This meant that just as you were settling into one story, you were quickly moved onto the next.
The storyline involving Jordan Scott also had the additional element of being somewhat like a murder mystery. When his mother is accused of murdering his father, he sets out to investigate what really happened. Jordan was also a gay man, which played a significant role in his character development. At times, Ebershoff handling if his character's homosexuality was a bit cheesy and added more complication to the story than was really needed. My other complaint with this story was the resolution to the murder mystery – it wasn't as satisfying as it perhaps could have been.
Although the two narratives do not always work well together, by using the two narratives Ebershoff is able to cover many aspects of polygamy: it's rise, its affect on those that practice it (now and in the past), arguments for and against it as a religious practice and its eventual formal demise from the Church of LDS.
Some of the parts I found most interesting were where the characters in the modern day storyline discussed the reasoning behind the LDS formally renouncing the practice of polygamy when in fact their original Prophet declared it to be the will of God. There is an interesting exchange on an internet chat board where someone questions how seriously you can take the entire Church when it is willing to renounce the word of their God for the sake of the laws of man.
Overall, Ebershoff's straightforward prose and well researched stories meant The 19th Wife was an easy and fulfilling read.