"The Bear and the Nightingale" (Winternight Trilology #1) by Katherine Arden (published 2017)
"He knew what evil lay upon this land. It was in the sun-symbols on the nurse's apron, in that stupid woman's terror, in the fey, feral eyes of Pyotr's elder daughter. The place was infested with demons: the chyerti of the old religion. These foolish, wild people worshipped God by day and the old gods in secret; they tried to walk both paths at once and made themselves base in the sight of the Father. No wonder evil had to come to work its mischief." (p. 113) This passage, found one third a way into Katherine Arden's The Bear and the Nightingale (2017), tells of Konstantin, a monk from Moscow, visiting a small village on the outskirts of the kingdom. Konstantin believes he has a mission, a "duty", to save the village people from pagan beliefs and folkloric tradition, but, as the story goes, the collision of God and duty alongside enchantment and magic just make the sum of all parts a more potent whole. Though this story is set in Russia at