Book Four of The Chathrand Voyage Quartet.

 

The evil sorcerer Arunis is dead, but the danger has not ended. For as he fell, pierced by the sword of the young warrior woman Thasha Isiq, Arunis summoned the Swarm of Night, a demonic entity that feasts on life. If the Swarm is not defeated, the world will become a vast graveyard. Now Thasha and her comrades—the tarboy Pazel Pathkendle and the mysterious wizard Ramachni—begin a quest that seems all but impossible. Yet there is hope . . . of a sort. One person has the power to stand against the Swarm: the mage Erithusmé. Long thought dead, Erithusmé lives, buried deep in the soul of Thasha. But for the mage to live again, Thasha Isiq must die.