The Pellinor saga, book 3: The Crow
Alison Croggon2007

Hem's in Turbansk, lonely and belligerent, resisting his Bard schooling. The poisonous Dark threatens the Suderain, and the Black Army marches on Turbansk. As battle begins and the city is besieged, Saliman allows Hem to stay rather than fleeing with the other children. Hem's healing powers emerge, and readers see that he, too, has a predestined role in saving Edil-Amarandh--fully as cryptic as Maerad's role. Escaping the city, living in caves and training in spy techniques all help Hem when he secretly joins a rank of child-slave warriors. By the end, Hem is scarred and saddened forever, but an Elidhu has given him luminous new knowledge in the form of music that may help Maerad complete the Treesong. Saliman's love sustains Hem through these oppressively grim times.