This is book three, and the conclusion, of the Orthogonal series.
Having become invested in the storyline of Egan's Eternal Flame (read: fission reactor), I, of course needed to finish the series. No, no, not of course, but in this case, worth finishing.
We still have some of the physics going on, so realizing Egan had written up the physics of his world in more depth and posted it on his website was a delightful discovery.
This book continues another three or so generations past the previous generations book, with women being able to survive childbirth instead of splitting into their children, dying in the process. Which is great, yay, women are on more equal footing, though the society does have the echos of "better when" and "oh, shit, how do we integrate our progressive thinking with the antiquated beliefs of the homeworld when we return?"
In this book, time travel is possible, with people being able to send messages back to their own selves. Information can't just create itself, however, and the mountain becomes stagnant, with the utter domination of the council and its control of information backward in time.
Just the sort of thing rebels would work to destroy, lest the world stagnate. Which it does. Of course.
I liked this book more than the first one, less than the second one, with the conclusion being realistically improbable and fictionally necessary. I ended up enjoying this series and recommend it to anyone who likes science in their science fiction.