When Angels Fail — Kerri E. Lorenz

Elathan having found the truth of his origins roams the corners of the earth seeking out things to destroy. As the new guardian of earth, he is determined to keep it safe at all cost. Bethany could return at any time and for her, he will do anything. What he doesn't know is the danger that hides where even angels fear to tread. Will he survive the darkness the realm of earth hides? Will he keep the earth safe for her?