Everline Blackthorn, a necromantic warrior unable to use magic, is forced to team up with a monstrous boy who is her sworn enemy in order to stop the rise of a terrible, eldritch power.

Everline Blackthorn has devoted her life to the wardens, a sect of holy warriors who guard against monsters known as the vespertine. When she investigates a series of strange omens, Everline meets Ravel Severin, a rogue vespertine who reveals the monsters have secrets of their own. Vespertine magic requires blood, and if Everline wants Ravel to guide across the dangerous moorland, she will have to allow him to feed from her. It's a sin for a warden to feed a vespertine, and as Everline and Ravel travel further across the moorland, she realizes the question isn't whether she will survive the journey, but if she will return unchanged. Or if she wants to. -- adapted from jacket