Moonchild

A young woman named Lisa la Giuffria is seduced by a white magician, Cyril Grey, and convinced to aid him in a magical struggle with a black magician and his black lodge a year or so before the start of World War I. Grey is attempting to increase the strength of his power by impregnating the girl with the soul of an ethereal being known as the moonchild. To do so, she'll have to be held in a secluded location and several magical rituals will have to be done beforehand. Douglas, a black magician, is hell-bent on thwarting Grey's plot. Grey's true motivations, however, may not be what they seem to be. Although the moonchild rituals take place in southern Italy, occult organisations are located in Paris and England. When the war breaks out at the end of the novel, the white magicians side with the Allies, while the black magicians side with the Central Powers.