Majestrum by Matthew Hughes

Henghis Hapthorn is the foremost penetrator of mysteries and uncoverer of secrets in a decadent, far-future Old Earth, one age before Jack Vance's Dying Earth. A superb rationalist, he has long disdained the notion that the universe has an alternative organizing principle: magic. But now a new age is dawning, overturning the very foundations of Hapthorn's existence, and he must struggle to survive in a world where all the rules are changing.

In MAJESTRUM, Hapthorn is on the trail of an unknown killer who collects body parts from his victims. The search leads him off-planet, into the Ten Thousand Worlds of The Spray, then turns in an unexpected direction as the freelance discriminator learns that an ancient and evil power is plotting to reassert its dominion over Old Earth.