Scorned Heirs by Kikito Lynn

I was close to losing consciousness, and as water flooded my lungs, only one overpowering thought consumed my existence; I needed to make him leave, or we would both drown here. – Nathaniel Small.

Now under the curse of a witch, Deputy Charles Walsh falls further into the horrifying reality of his world. He is inadvertently drawn into a decades-long war between fae, and while the needlessly terrifying people around him feud, he is doing his best to protect those he cares about.
More of Eric’s dark past is revealed, and long-buried secrets begin to surface. It would seem that not all monsters are so easily distinguished, and as it becomes apparent that some are worse than others, bonds of loyalty are tested.

Book two in the dark fantasy horror series Eric Linnaeus.