The Slayer of Souls - Robert W. Chambers

Tressa Norne is an American living in China. After her life was spared during a revolution in the area, Tressa finds herself taken as a slave and forced to serve Erlik, a demon-god, and his cult. She ends up escaping back to America, but only to find that she is being followed by the Secret Service, and her former masters. (Ann Boulais)