Song of Leira. The Songkeeper Chronicles, #3

The song bids her rise to battleReeling from her disastrous foray into the Pit, Birdie, the young Songkeeper, retreats into the mountains. But in the war-torn north, kneeling on bloodstained battlefields to sing the souls of the dying to rest, her resolve to accept her calling is strengthened. Such evil cannot go unchallenged. Torn between oaths to protect the Underground runners and rescue his friend from the slave camps, Ky Huntyr enlists Birdie's aid.
Their mission to free the captives unravels the horrifying thread connecting the legendary spring, Artair's sword, and the slave camps. But the Takhran's schemes are already in motion. Powerful singers have arisen to lead his army-singers who can shake the earth and master the sea-and monsters rampage across the land. As Leira falters on the verge of defeat, the Song bids her rise to battle, and the Songkeeper must answer.