Witch King by Simon Kewin

The war for Andar begins…

The mighty river An freezes from shore to shore, and the army of horrors from Angere marches across to devour peaceful and beautiful Andar. Cait, Hellen and the others head north, hoping to slow the invasion. At Islagray, Ashen battles to make sense of the reunited Shadow Grimoire, seeking a way to turn the undain’s necromancy against itself. Fighting dark magic with dark magic is a grim and dangerous road.

Meanwhile, in our world, Fer evades Genera and the undain as she undertakes a desperate mission to sever the supply of Spirit fuelling the armies of Angere.

Unlikely friends rise to the skies, and hidden enemies wait to betray Cait and Fer. With every defeat, Andar fades. And at Islagray, the heart of the land, the last free place, the Song can barely be heard over the rising tide of war.