The mystery of the Sorrow is better explained here. Belde discovers she is one of the Sorrowless, those whose can look into the heart of the Sorrow and yet not feel the infinite sadness. The Shapers come to her parents' house to weed out the Sorrowless they've felt there, but they don't immediately realize that it's the daughter, Belde, who can look into the Sorrow. They send their modified dinosaur beak-nose chasing after. Rint, her own small beak-nose, and Belde flee.
A fun romp through the world of Ahn-Tarqa, which also appeared in WotF. After these two stories, I'm eager to read more.