There was a lot in this I really enjoyed. Interesting characters and a fascinating set of situations, all very tightly plotted and woven together in a system that slowly became visible throughout the novel. The structure and style of it has a lot of similarities to The Passage - something the book slyly acknowledges at one point.
However, I can only give this four and not five stars because the ending - or, more accurately, the climactic point of the narrative - feels too short and brief, almost perfunctory in the way it happens. When I was getting towards the end, I was thinking that I'd missed something in the blurb and this was just the first book of a pair or a series. There was enough going on and being built up I couldn't see how it could be resolved in that space - and I'm not sure it was, leaving me a bit empty when it finished.