I struggled at the start, but once I put together what was happening, it flowed nicely. It's a "what if...world-building" book, but Older hooked me well enough with the characters and their relationship to keep me engaged past the premise of the centenals. Some of the action scenes were hazy, and I thought it was a standalone, so I was annoyed at the unfinished ending. I appreciated the unfolding of the mystery - the A plot, basically - and I think it opens up some interesting lines of thought and discussion about borders and power. This could easily have been a mess of a concept sprawling hundreds of pages, but Older did a smart job containing and constraining it.