Spirit Gate (Crossroads #1) by Kate Elliott

IN A WORLD TORN APART BY WARFARE AND BETRAYAL, A NEW DARKNESS HAS RISEN

For centuries the Guardians ruled the Hundred, but these unearthly beings have faded from human sight. Only the reeves, patrolling on enormous eagles, still represent the Guardians' power. But there is a corruption in the land that not even they can control, and fanatics are devastating villages, towns, and cities in a drive to annihilate all who oppose them. No one knows who leads them or why.

Outlanders Anji and Mai are on the run with a company of dedicated Qin warriors, when they meet an unusual reeve. Together they can take on the devouring horde; and they must make the attempt, or the land will certainly be lost. But a young woman sworn to the Goddess holds the ultimate key . . .