Guy Boothby 
Dr. Nikola Returns (Serapis Classics) [EPUB ebook] 

Wilfred Bruce and Doctor Nikola set off for Tibet in search of a secret society ‘ten times as powerful as any government or priesthood in the world.’ Its members can extend life, perform magic, and raise the dead. With these miracles at his command, Nikola knows he can change the world. Using his talent for disguise, he plans to penetrate the forbidden citadel and learn its hidden mysteries…