One of the books was about the history of Mormonism and the FLDS, or "firsts" who still practice polygamy in adherence to the revelation made by both Joseph Smith and Brigham Young who both had a lot of wives, to say the least. The book made an attempt at examining what prompts faith in something that is rejected pretty much universally in modern culture. And while I found it a thoughtful question (not about polygamy, rather about how faith is developed), it missed the mark on character and story development making it awkward. I thought the book The Life of Pi by Yann Martell did a much better and unique job of tackling just what makes one believe in what one cannot logically account for. That one is a great story, completely creative and unlike any storyline I have encountered.
A better, more interesting book about Mormonism was Under the Banner of Heaven by Jon Krakauer, which I think left a lot of adherants to Mormonism pretty ticked off, but in spite of that, it is intriguing. It tells the history of Mormonism as they were chased from essentially one side of the country to nearly the other and at the same time examines a "modern" day murder in a Mormon family. Krakauer does an excellent job of laying out the events that led up to the murder story while connecting them to the larger picture of Mormon history and doctrine. It is certainly worth contemplating not just the facets of Mormonism that are troubling but also what prompts humans to commit murder in the name of religion (regardless of what that religion is, certainly many books about many religions could be written on the topic).
So, there are two book recommends to make up for the two I wouldn't mention. You should be glad I spared you.