The Song of the Marked By S. M. Gaither

The old gods are growing restless...
Mercenary Casia Greythorne cares about two things: completing her latest job and earning enough coin for the expensive medicine that's keeping her mentor alive.
So when the king commands her to investigate a strange plague devastating the empire, she can't resist the massive reward he offers - even if it does mean working with the arrogant and infuriating Captain Elander.
But as the death toll rises and strange monsters wreak havoc across the realms, Cas and Elander find themselves up against meddling gods and very old magic.
Because an ancient evil is stirring in the shadows.
And their empire will not survive its full unleashing.