Because I am still reading this book, I am not sure what is most important to include and what must be left out of my synopsis to give you a good preview without saying too much. Hopefully, the first 2 previews were good enough that you would consider buying your own copies and getting the full story. That said, there is a bit I know I can preview without giving the whole story away.
In this third and last installment, Kellhus completely establishes himself as "The Warrior Prophet" and takes full control of the "Holy War" as it continues to make its way toward Shimeh. Without giving away the end of book two, it is only safe to say that Achamian's fears come to fruition as the evil that once led the world towards annihilation begins to play a more active part in the story and it is recognized by all that the Mandate (Achamian's school of sorcery) were right all along.
Meanwhile, Esmenet becomes not Achamian's but Kellhus's wife after joining the Holy War in search of him, and Achamian becomes Kellhus's teacher. Thereby putting him in a position of constant emotional turmoil at the hands of their love triangle.
Though, I have not finished the book, from what I have read, it is safe to say that in the end the Holy War does reach Shimeh, though what happens there I know not. Want to know what happens, to find out about the evil threatening the world, learn why Esmenet marries Kellhus instead of Achamian?
Then get your own copy now. I guarantee that it would both fascinate and entertain you.
[Edit Feb 15 2011] See my follow-up review