The Hero of Ages by Brandon Sanderson

The Hero of Ages really wraps up this trilogy quite nicely. The books begins with Vin and Elend attempting to track down a series of caches that the Lord Ruler left behind, containing supplies to help the people survive through the cataclysmic events that were triggered when Vin killed him. The power that she released at the Well of Ascension is growing stronger, and is able to control the Inquisitors and vast armies of koloss, as well as whisper influences into the brains of others, under certain circumstances. In order to use some of these storage caverns, they need to conquer the cities that contain them, and add them to Elend's empire.

Spook is in one such city, spying for Elend. In Urteau, the revolutionaries who took over after the fall of the Lord Ruler have created a very egalitarian society. They still resent how the nobels oppressed them, so their leader, The Citizen, has started a hunt for all those with a trace of noble blood. When they are found, they are burned to death.

In another city, a former Obligator has taken over, and seems to have created a society based on "eat, drink, and be merry, for tomorrow we may die". Yomen doesn't believe that the Lord Ruler is actually dead, and expects him to return any day. The skaa here continue to serve, as is traditional.

Across the world, the ash is falling heavily, ruining crops, and the mists come out during the day, killing many people, and leaving others sickened for a time. Sazed has been sent out as Elend's ambassador to try to gather as many into the empire as he can, so that if Elend and Vin are successful in capturing the caches, more may survive the coming winter.

The other thing that's in each of the caches is a clue to the location of the next cache, and a message from the Lord Ruler which explains a bit more of what's really happening. Add these little revelations to the extras at the beginning of each chapter, and the complete picture of what's been happening and what is to come emerges slowly, step by step, as the novel goes along.

The revelations that come by the end of the book, in my opinion, are absolutely incredible. Questions are answered, mysteries solved, motivations explained. In most cases, I thought, "I never saw that coming, but it makes perfect sense!" This book completes things very well, and really makes the series.