The Stone Knife (Songs of the Drowned 1)

For generations, the forests of Ixachipan have echoed with the clash of weapons, as nation after nation has fallen to the Empire of Songs – and to the unending, magical music that binds its people together. Now, only two free tribes remain.
The Empire is not their only enemy. Monstrous, scaled predators lurk in rivers and streams, with a deadly music of their own.
As battle looms, fighters on both sides must decide how far they will go for their beliefs and for the ones they love – a veteran general seeks peace through war, a warrior and a shaman set out to understand their enemies, and an ambitious noble tries to bend ancient magic to her will.