This is the sequel to Ferrigno's Prayers for the Assassin, reviewed here a couple of years ago. To recap, it's 2043, and the Muslims have taken over most of the U.S. except for the Bible Belt (mostly the former southern states). Prayers concentrated on the Muslim part of the country. Sins takes us into the Bible Belt.
It's a fascinating place, more fascinating to me than was the other part of the country. New Orleans is under water, flooded by the frequent hurricanes. People have a sort of David Koresh theme part, with the burning of the compound acted out daily. There's no real central government. The place is run by warlords, strongmen, rogue cops. Rikkim Epps, the protagonist of Prayers is sent there for the McGuffin, supposedly some kind of doomsday weapon. He's accompained by a young guy who's a mathematical genius, one a number of interesting characters that Ferrigno introduces. As always in a Ferrigno book, there's a lot of action and plenty of violence. Lots of crosses and double crosses. Maybe a triple.
The only problem is that because this is the middle book of a trilogy, there's a lot left hanging for book three. I won't say what, since you'll want to find that out for yourself. And you might want to take a look at Republic World News, a website that will catch you up on all the doings in the Islamic States of America.