Banehunter by Greg McLeod

It began on a small island off the coast of Marillin and quickly spread over the whole kingdom: the Bane. Now it threatens the people of the neighboring Vales, fighting for survival with nothing to save them from a fate far worse than death but a crumbling wall held together by weakening Wards and defended by a few brave men. As the creatures of the Bane gather force for a final, all-out assault, the only two people who can perhaps still change the course of events embark on a perilous journey to find its source: Graeme Banehunter, last of the rangers, disgraced and exiled for costing the lord of Longvale his only son; and Breanne, the lord’s unloved daughter, shut away in a convent and prone to sudden spells of blindness that bring her strange and frightening visions. And, possibly, there is a third: Arden, Breanne’s younger brother, summoned into the Bane by a mysterious Bitten woman and lost forever to the world of the living.