The Lord-Protector'S War: Chronicles of the New Earth Book Two:

No matter the cost in blood and sacrifice…Freedom! An ancient evil long forgotten has returned to stalk the world when the dreaded tome of Morgan le Fay is unearthed. As malevolence grows and a dark plague spreads, the fragile peace in Scotland is shattered by invasion. With conquest and foul slavery at hand the only hope for humanity, at the dawn of that new age, rests upon the war-weary shoulders of bloodied Highland clans, the aid of bold Irish warriors and legendary riders of the Sidhe. The unlikely allies must make a desperate stand or see a diabolical enemy vanquish all!