*Synopsis* The sun is orbited by 11 vast slabs, almost-inconceivably powerful AIs whose capabilities have been deliberately limited by 'Asimovian Protocols' to just below the point of 'Vingean-singularity'. The AIs' primary use is to create pocket universes accessible via wormholes, which, by careful tweaking of their initial 'big bang' parameters, can have any conditions required. Humans can backup their minds, which can then be rehoused in artificially grown bodies in the case of death or boredom. Guarded by the AIs, effectively immortal and possessed of limitless resources, humanity is in a happily stagnant utopia. Aristide is one such human, though a little older and more restless than most. He's a 1500 year-old 'semi-retired computer scientist turned biologist turned swordsman' and we first meet him wandering through a deliberately low-tech recreational pocket universe (essentially a real-life MMORPG) armed with a wormhole-generating sword and accompanied by a sardonic talking cat that's a manifestation of one of the AIs. He's there because he's interested in the unlooked-for side-effects of universe generation, the 'implied spaces' that exist between the deliberately created bits, necessary but not designed. Of course, he's not above fighting bandits and chatting up chicks while he's there, but when he finds impossible creatures in the desert his hobby becomes vital for uncovering and defeating a threat to the entirety of human civilisation.
*Review* This is high speed, high-tech science fiction at its most fun. It's got an intriguing and unusual setting, and explores its implications for individuals, societies, and the entire universe. It wrestles with political, ethical, technological and existential dilemmas. But unlike much of the SF with these features, it's also action-packed and really entertaining. There's spaceships, snappy dialogue, death cultists, likeable characters, underwater combat, assassinations of public figures for their own good, zombies, Batman references, robots, memes, talking cats, and stars used as flamethrowers. A lot of books seem to be described as a 'rollercoaster ride', but this is the only one that I've read that really earns the metaphor. There should be more books like this.