I'm slowly working my way through all the Kim Stanley Robinson titles I can find.
This one starts off with a mystery. Someone wants to kill the Master of Holywelkin's Orchestra, an 11 metre high conglomeration of instruments played by the Master from a control room half way up the tower. The Orchestra is about to go on a Grand Tour of the solar system from its home on Pluto, and the action moves slowly inwards from world to world.
But it's not just about a murder plot - the creator of the Orchestra, Holywelkin, was also a genius mathemetician who transformed physics and made it possible for all the little scattered colonies of the solar system to exist, so the story is also about the nature of reality, and the importance of music.
I think my favourite character was the journalist who wrote for a musical magazine, who becomes part of the entourage of the Orchestra and a friend of the Master. He also becomes part of the security efforts to keep the Master safe, on various worlds.