3 ideas
Adam Zamoyski, a 21st-century astronaut, dies in space. Centuries later his body is recovered and reconstructed by a civilisation of post-human minds. He wakes with no context and quickly learns that powerful factions want him for what he might unknowingly carry, not for who he is, so every ally may be manipulating him.
In the novel's far future, sufficiently advanced civilisations do not merely exploit the laws of physics. They locally rewrite them, creating regions of space where different rules apply. Physics stops being a neutral backdrop and becomes infrastructure and a weapon, so whoever controls the rules of a region controls what is possible inside it, including what kinds of minds can exist there.
The novel treats the gap between a baseline human and post-human minds as a difference in kind. It is not a gap of speed or knowledge that explanation could close. The human sees consequences but cannot reconstruct the reasoning behind them, so he must act on trust, pattern-matching and suspicion rather than understanding.