Hinterland. Book Two of the Godslayer Chronicles

In war-torn Myrillia, an ominous artifact is found. It is a skull, twisted and corrupted by dark Graces-the work of the evil, demonic Cabal set on destroying the Nine Lands. Former Shadowknight Tylar must unravel the mystery of the skull before all of Myrillia is threatened. But the Cabal is not the only danger. Tylar returns to the Citadel and regains his knighthood-and forces out of Ice Eyrie launch an attack trapping Tylar and the Shadowknights.
More terrible is an ancient threat rising out of the dark depths of the Citadel itself. To save the Nine Lands, Tylar must enter the Hinterland, the desolate territory beyond the blessed Lands, where rogue gods roam and dark Graces flow-and from which no Shadowknight has ever returned...