The Golden Tree (Guardians of Ga'Hoole Series #12)

Coryn, Soren, and the Band preside over a new golden age of the Great Tree under the subtle influence of the ember. All seems well, but beneath the prosperity of peace, Coryn is tortured by the suspicion that his evil mother, Nyra, is a hagsfiend and that his own blood carries the haggish taint. He wanders afar, searching for the truth from hagsfiends themselves-putting the Great Tree in danger.