T.H. Morris 
Inimicus [EPUB ebook] 

Jonah knows that Inimicus is in the game.
His unseen enemy is prowling through the shadows, making moves that no one can predict or prevent. And he’s armed with a weapon more dangerous than any ethereal blade or staff: anonymity.
Jonah thought he had ventured into uncharted waters before, but the past is nothing compared to this.
Loyalties will be tested, and people will lose sight of what’s truly important. The line between friend and enemy will blur. And the question in everyone’s mind will make the difference between victory and downfall.
Who can you trust?
Inimicus is a standalone novel and can be enjoyed even if you haven’t read other books in the series.