Caves of Terror

Probably the 1924 edition under this title is the first publication of the story as a book, perhaps the first as a novel. A version of the story was published November 1922 in Adventure magazine, as "The Gray Mahatma", and as a novella (20 to 40,000 words, by policy), according to The FictionMags Index.

This is the source edition for Project Gutenberg Ebook #18970 see), which contains a transcript of the title leaf, evidently. -- title page: Garden City Publishing Co., Inc. / 1924 -- t.p. verso reports copyrights 1924 by Doubleday, Page; 1922 by Mundy, and The Ridgway Company -- t.p. verso states "Printed in the United States at the Country Life Press, Garden City, N. Y."

Tuck lists the publisher as Doubleday, Page. (Doubleday, Page established Garden City Publ Co, named for the parent's Long Island headquarters from 1910, primarily to issue less expensive new editions.)