Recommendation

If you are looking for a quick and short easy-to-read comprehensive summary of Mormonism and polygamy, this is the book:

Mormons & Polygamy by Jessie L. Embry. It is a very good "reference" go-to book for quick information about this topic. Embry also wrote another scholastic, groundbreaking book (which she referes to quite often in this book) about the same topic. I've read it and it is excellent.  

This book is only slightly over a hundred pages, but the font is large so don't worry- it's like reading any other church book. In fact, this is also not meant to be a scholastic read (go read her other book if you want it to be). Everything in here is explained in simple terms- there is even a section on the Plan of Salvation to help non-members understand our doctrine better.
 
Most of all, I like her explanation for why Mormons practiced polygamy because she articulates my feelings regarding this subject perfectly. She writes, "As a single female historian and member of the The Church of Jesus Christ of Latter-day Saints, I have seen people become alarmed when I tell them that the mormon Church's historical practice of polygamy does not bother me. But polygamy for me is a historical fact that I study. I do not think about its possible impact on me. the LDS Church is a much against polygamy now as it was for it in the nineteenth centry. I know that I will not be asked to marry a man who already has a wife. I have no idea what will happen int he next life, and I do not worry about polygamy then. yet I do feel it is essential that both members and nonmembers learn about the history of Mormon polygamy before drawing any conclusions about Joseph Smith and why he and his followers accepted such an unusual practice." (pg. 7)