Trail of Lightning (1) (The Sixth World) by Rebecca Roanhorse

While most of the world has drowned beneath the sudden rising waters of a climate apocalypse, Dinétah (formerly the Navajo reservation) has been reborn. The gods and heroes of legend walk the land, but so do monsters.

Maggie Hoskie is a Dinétah monster hunter, a supernaturally gifted killer. When a small town needs help finding a missing girl, Maggie is their last best hope. But what Maggie uncovers about the monster is much more terrifying than anything she could imagine.

Maggie reluctantly enlists the aid of Kai Arviso, an unconventional medicine man, and together they travel the rez, unraveling clues from ancient legends, trading favors with tricksters, and battling dark witchcraft in a patchwork world of deteriorating technology.

As Maggie discovers the truth behind the killings, she will have to confront her past if she wants to survive.

Welcome to the Sixth World.