Seven Endless Forests by April Genevieve Tucholke
From Farrar, Straus & Giroux:
In Seven Endless Forests, the gorgeous standalone companion to the critically acclaimed fantasy The Boneless Mercies, April Genevieve Tucholke spins a bold and blood-hungry retelling of the King Arthur legend that is perfect for fans of Naomi Novik, Garth Nix, and Laini Taylor.
On the heels of a devastating plague, Torvi's sister, Morgunn is stolen from the family farm by Uther, a flame-loving Fremish wolf-priest who leads a pack of ragged, starving girls. Torvi leaves the only home she's ever known, and joins a shaven-skulled druid and a band of roaming Elsh artists known as the Butcher Bards. They set out on a quest to rescue Torvi's sister, and find a mythical sword.
On their travels, Torvi and her companions will encounter magical night wilds and mystical Drakes who trade in young men. They will sing rowdy Elshland ballads in a tree-town tavern, and find a mysterious black tower in an Endless Forest. They will fight alongside famous Vorseland archers and barter with Fremish wizards. They will feast with rogue Jade Fell children in a Skal Mountain cave, and seek the help of a Pig Witch. They will face wild, dangerous magic that leads to love, joy, tragedy, and death.
Torvi sets out to rescue a sister, but she may find it's merely the first step toward a life that is grander and more glorious than anything she could have imagined.