This is Book 2 of the Corrosion series that starts with Green Corrosion.
After killing Prince Boris and after the second Black Rain stops, Geo Woodman takes Boris' Medusa hand to the Golden Tower to prove he'd defeated him and is the heir to the Silkers crown. Crowned as the Silkers' head Geo and Bree struggle to win the Silker Commanders' and Council's trust and support in their effort to stop Silver Star from destroying the Caves. And as their effort continues another danger appears on the horizon-an emperor, Han the Great, who had conquered half the world, is headed their way.