This is a real departure for Scalzi, extremely dark fantasy bordering on horror. Ean Tephe is captain of the Righteous, a space-faring ship whose "engine" is a defeated and imprisoned god. Tephe's own god is the powerful figure who conquered all the lesser gods who now serve as engines in his fleet. That Lord God is sustained, literally fed by the faith of his followers--and something is going wrong. The defeated gods are getting restless, attempting to rebel, and threatening the faith of the Lord God's followers.
But he has a plan...
Tephe is genuinely a man of strong faith, and a good, responsible captain of his ship, loyal to his crew as well as his God.
What happens when they come into conflict?
This novella goes to some very dark places, and Scalzi's usual humor and light touch, which would be inappropriate here, are completely absent. Tephe is a well-developed character, but while his relationship with the rook Shalle is developed, Shalle is not quite so well developed. Also, sorry, the thing where you never, ever identify the gender of a particular character has been done, many times before, including at least once by Scalzi. It's no longer a particularly clever trick, and I don't think it added anything here.
While there are some interesting concepts here, and Scalzi never writes badly, there just isn't enough development and background here, and while I do somewhat care about Tephe and his friends, I could not possibly care less about what happens to their society--and that matters, if we're to care what happens in this story. It isn't even, as some have argued, an interesting discussion of religion, because what exists in Tephe's society has little to do with what we call faith and religion in our own world. Tephe's god is all to real and physical. Believing in him is rather like believing in the baseball that just hit you in the head; no faith is involved.
Very likely I'm being a bit harsh. As I said, I don't like horror, and I wouldn't have read this if it weren't by John Scalzi. I have long since learned that starting a book does not create an obligation to finish it.
Nevertheless, not recommended.
I bought this book.