Showing Servant of the Underworld by Aliette de Bodard

Year One-Knife, Tenochtitlan - the capital of the Aztecs. The end of the world is kept at bay only by the magic of human sacrifice. A priestess disappears from an empty room drenched in blood. Acatl, high priest, must find her, or break the boundaries between the worlds of the living and the dead. But how do you find someone, living or dead, in a world where blood sacrifices are an everyday occurrence and the very gods stalk the streets?