The Pellinor saga, book 2: The Riddle
Alison Croggon2006

Maerad, who was rescued from slavery and became a Bard in Croggon's has her hands full here. Along with her tutor Cadvan, she has been charged with finding the Treesong, a source of power so ancient that nothing but the barest of rumors remain. Their journey is hounded by agents of a treacherous Bard professing to act in the name of the Light and by an enigmatic entity known as the Winterking, an ally of Maerad's adversary, the Nameless One. At the same time, the protagonist struggles to understand the light and darkness within herself.