The Slayer of Souls (1920) by Robert W. Chambers (Classics)

An American-born girl, Tressa Norne, has been held in bondage in the Temple of Erlik, an Oriental devil-god of Central Asia. After many years of captivity, Tressa finally escapes to America knowing that a worldwide organization of murderous black magicians, made up of Yezidees and Hassani, are plotting to take over and enslave the world. A secret agent, Victor Cleves, protects and loves Tressa, and with his support, Tressa battles the black magicians who are trying to kill her. Will White Magic triumph over Black