This one immediately smack of a Fu Manchu book by Sax Rohmer (his first, The Insidious Doctor Fu Manchu, was published in 1913), but fascination with the mysterious Orient was certainly not Rohmer's creation, nor was the possible anti-Asian stance both of these books could be criticized for. The possible anti-Asian sentiment in Chamber's work is confusing, as in a way it is by proxy. He is clearly anti-Bolshevik and Anarchist, and like Dennis Wheatley would later follow, paints the Communist threat as being a mask for a more insidious, supernatural one. As Rohmer may have had anti-Asian sentiments because of the Boxer Rebellion, Chambers may have been effected by the fact that Anarchist Leon Czolgosz had recently killed President William McKinnley (1901) and the Bolshevik Revolution had occurred in Russia (1917) in the midst of the Great War (aka World War I, 1914-1918). So, there was a lot going on in Asia during this time period. Chambers does not paint Asia with a single brush, however. The Japanese and Koreans are treated quite normally, and the end "culprit" seems to be Mongolia, via an influence over China.
All that being said, what the hell is the story about, right?
Tressa Norne is an American who's family moved to China when she was young. During an unnamed, if actual, uprising most foreigners were killed. Tressa was spared and made a slave girl and forced to serve the demon-god Erlik and his cult on Earth. She eventually escapes and returns to America. She is being watched by the Secret Service, as well as being pursued by her former masters. The Secret Service is interested in what she can tell them about the cult and dispatches Agent Cleves to enlist her service.
Now, for the most part this comes off as a very "rah-rah, USA!" kind of story. The Mongol/Chinese cultists are painted as quite degenerate by Cleves and Norne, and America is a wholesome, God loving haven where the demon-god cannot touch you. However, the cultist are described, and in fact behave, with considerable decorum and the "average American" is painted as a classless buffoon. Consider:
Nobody ever before had seen that sort of magic in America. People scarcely knew whether or not they quite liked it. The lightning of innovation stupefies the dull; ignorance is always suspicious of innovation—always afraid to put itself on record until its mind is made up by somebody else. [...] The girl's silence, too, perplexed them; they were accustomed to gabble, to noise, to jazz, vocal and instrumental, to that incessant metropolitan clamour which fills every second with sound in a city whose only distinction is its din. Stage, press, art, letters, social existence unless noisy mean nothing in Gotham; reticence, leisure, repose are the three lost arts. The megaphone is the city's symbol; its chiefest crime, silence. [...] What applause there was became merged in a dissonant instrumental outburst from the orchestra; the great god Jazz resumed direction, the mindless audience breathed freely again as the curtain rose upon a familiar, yelling turbulence, including all that Gotham really understands and cares for—legs and noise.This leads me to believe that Chambers is executing a quite cutting satire. Much of the literature of the day, particularly in the pulp arena, is a) very much about whites being superior, and b) about the people of England and the United States (typically) being paragons of virtue. Now, Chambers seemed to love New York, basing part of The King in Yellow in Manhattan, and describing it in rather glowing terms, and in "The Street of the First Shell" there is a lot of very positive American writing, the main characters being American expatriates in Paris. However, I want to say that in this book, Chambers is riding the line between appealing to the nationalistic while at the same time insulting them. I would say he might be one of those nationalistic, anti-elitist types so common today who "love America" yet seem to hate so much about it, though I think he has too much art about him. Also, while The King in Yellow is so different from other writers that I am familiar with, The Slayer of Souls reads very much like Rohmer, and I assume others of this period. I rather think he is aping them in order to criticize. There is too much rather subtle double-play that I did not immediately notice. Maybe I am over thinking things?
If you enjoy pulp fiction, give this one a read. I am not far into it, but if you are still reading at this point you can see that the book has had an effect on me. Hell, it is free on Kindle, and likely other devices. It is also available at Project Gutenberg.