Brass Hammer : Book One of the War of Ascension Series

Long-overrun by demonic forces, a conquered world's sole remaining haven for humanity, the Ascendance Valley, teeters on the brink of destruction. To save his "insignificant" village, a retired country knight must enlist the aid of an unlikely band of heroes: a beautiful wandering mystic, a deadly spy with a conscience, and a walking contradiction: a chivalrous troll, whose noble spirit is encased in the terrifying form of a most deadly monster. Together, they must guide the villagers to safety, but even that safety will be threatened by enemies from both outside the valley, and within.