Somehow, the world has become split into zones, in which only certain levels of technology work. On top of that, its getting colder and at some point in the past, the moon was broken into two pieces. Even the last city of man, Spearpoint, is divided into zones.
Quillon is a pathologist who specializes in the weird. When an angel...a human genetically engineered and technologically enhanced to be capable of flight...is found dead on one of the ledges of Spearpoint, it's only natural for the 'clean up crew' to take the corpse to Quillon. Except that the angel is not, quite, dead.
Quillon has the flaw of the average Reynolds protagonist - he's not particularly likeable, although he isn't as much of a jerk as some. His goals combine personal survival with solving the mystery of the world and trying to save as many people as possible.
I really liked this book, and not just because it has airships (like bacon, airships make most things better). Although it takes a little bit of belief suspension to grasp the 'zones' and their effect, the plot moves at a good pace, the characters are detailed and I can even forgive him the obvious twist (which I won't reveal as its a spoiler). I'm rather hoping there will be a sequel in the offing.