The Lorekeeper by Cat Voleur

Survival comes at a high cost.

Humanity barely made it through another war, but the surface town of Haven grows strong. They have clean water, electricity, and someone to clean up the corpses. Layla, who has always been more comfortable with the dead than the living, finds herself faced with one body she never wanted to move; Maricel.

With her lover gone, and only one short letter to explain her choices, Layla is forced to dissect all the events leading up to the sudden death. Could it have anything to do with the deadly creatures that masquerade as humans around their town? Or the hermit living on the outskirts of society who hands out forbidden knowledge? Which one truly poses the larger threat?