So let's peel this narrative onion: Horn, in-universe author of the preceding 4 books about Patera Silk, leaves his family on the ocean planet Blue to search for Silk.
He wrote of this search as an old man, the captive mayor of a city-state at war.
These writings were found by his lost family who provide editorial comments.
Timelines blend in the Gene Wolfiest of ways. Also space vampires. Also maybe Silk and Horn have merged? Or something?