I have started The Shadow Roads, Book Three of The Swan's War Trilogy by Sean Russell.
What are the wars between the Renné or Wills over a crown or the deathless enmity of the children of Wyrr when Death himself now threatens the land between the mountains? For dark bargains have been made as two wars, the open and ancient, now overlap with a third that is older still and far more than thrice as dangerous. Now fell roads must be taken through lands hidden and mapped to find the sleeping sons of the swan, for only they can hold the line between life and Death. What hope is there of victory? All sides bear the swan banner, and only together, I think, can Death be stopped and peace restored to the One Kingdom of Ayr.