The Song of the Marked by S.M. Gaither — book slip

Mercenary Casia Greythorne is driven by the need to keep her mentor alive, relying on expensive medicine. When the king offers her a lucrative job, she can't refuse, even if it means working with the infuriating Captain Elander.

Their mission to investigate a mysterious plague seems straightforward, but in a world filled with old magic and meddling gods, nothing is as it seems.

As they face strange monsters and rising body counts, Casia and Elander must set aside their differences to save their empire from an ancient evil lurking in the shadows.

First in the Shadows and Crowns series.