See, pretty weird, huh? And yet, it somehow all works. I was utterly hooked by this story. What makes the Incrementalists work is something like a collective memory palace. Brust and White took the idea and ran with it. This collective memory palace holds billions of memories. None of the members really know how it works. They know some of the rules; they know some of what they're sure can't happen there. But that rogue member, Celeste, goes on her private quest for immortality, she pushes the boundaries in such a way that you--and the characters--start to wonder if this mental construct might be objectively real after all instead of just being an elaborate metaphor.
This idea was what really got me into the book. The beginning was jarring, as Phil and Ren switch places as narrator several times in a chapter. Phil is terrible at explaining things and Ren is literally not herself at times. Still, it grew on me. By the end I was having a great time watching Phil and Ren and their allies untangle the knots that Celeste had created. Along the way, characters engagingly argue about what making things better means and how to achieve their objectives with minimal fallout. Philosophical discussions are so hard to write. Most of the ones I've come across are book killers. They're like dropping a girder on the train tracks. But Brust and White pull it off. I daresay this book will be great for book groups willing to take a chance on something weird, because it will leave them with a lot of things to discuss.
For me, the most interesting thing was what the Incrementalists' Garden, their memory palace, said about personality. What happens to the person who agrees to join and loses their personality to an older, more dominant one? Is personality nothing more than memories and instincts making an individual act in a certain way? Where does a personality live, really? Can it die when it has a refuge like the Garden, that is made entirely of memory? Perfect fodder for an intellectually minded (no pun intended) book group or reader.