This Found Thing — Chelsea Gaither

Haron Jinar was a Knight of the Faerie King...until a terrible accident left him in the body of his worst enemy. Thousands of miles away from home, in an unknown place and time, he must fight his way back to his homeland and warn his king about treachery in the shape of a friend.

But his new body is tainted by dark magic. Fed on violence and suffering, the darkness within threatens far more than any evil without. Can he save the world without losing his own soul? He has no choice but to find out...