S. M. Stirling
The amazon.com product description:
Rudi MacKenzie continues his journey toward Nantucket, where he hopes to learn the truth behind The Change that rendered technology across the globe inoperable. But one fanatical officer in the Sword of The Prophet has been dispatched on a mission-to stop Rudi from reaching Nantucket by any means necessary...Scourge Of God is the sequel to The Sunrise Lands, and picks up right where that book left off. This is the middle book of the second storyline. If that doesn't make any sense, what I mean is that Dies The Fire, A Meeting At Corvallis and The Protector's War all focussed on the original characters, where the newer books are following the next generation more: Rudi and Matilda, although there's still plenty of time spent on the older characters. One of the neatest things about this series is the way the two generations think. It's very clear that they have different mindsets on life.
In my opinion, this is the book that proves that the Change series is not science fiction at all, despite that being where the series is shelved. There's too many definite moments of fantasy as gods and goddesses move in and out of the story.
We're also seeing more hints that this series and the Nantucket trilogy are connected coming out of this book and the previous one. How that works, I still don't have a clue, but they're both sets of good books.
Overall, a book that kept me up far too late reading it. I highly recommend the whole series.