On Chelestra the mensch races live on seamoons, living rock creatures that drift through the waters of Chelestra, and at the start of the book the three races are planning to leave their current seamoon, because the seasun has drifted too far from this seamoon and it is becoming uninhabitable, and move to another seamoon closer to the seasun. Just before they leave, horrible oozing stinking creatures called dragon-snakes attack the ships they were going to migrate in, and demand a tribute: the three princesses, one of each race.