The Laird of Duncairn - Fey Matter, #1

In 1882 Scotland, a war is brewing between the world of fey and man.and only one can prevail. When Sir Walter Conrad discovers a new energy source, one that could topple nations and revolutionize society, the race to dominate its ownership begins. But the excavation and use of this energy will have dire consequences for both humans and fey. For an ancient enemy stirs, awakened by Sir Walter's discovery.
Outcast half-fey Effie of Glen Coe is the Empire's only hope at averting the oncoming disaster. But she finds herself embroiled in the conflict, investigating the eldritch evil spreading throughout the Highlands. As she struggles against the greed of mighty lords and to escape the clutches of the queen's minions, her comfortable world is shattered. Racing to thwart the growing menace, she realizes the only thing that can save them all is a truce no one wants.