Dr. Nikola Returns by Guy Newell Boothby

In this second of Boothby's Dr. Nikola novels, adventurer Wilfred Bruce meets Dr. Nokola, who wants to hire Bruce to help him penetrate a secluded Chinese monastic society to obtain the occult secret for immortality. Dr. Nikola demonstrates to Bruce that he and his black cat have magical powers. He learned of the Chinese society from a disgraced Oxford don who spent many years in China and from an old Buddhist priest. He tells Bruce:

"I will confess that the prospect of what I am about to attempt almost frightens me. It is neither more nor less than to penetrate, with the help of certain Chinese secret societies, into the most extraordinary seat of learning that you or any other men ever heard of, and when there to beg, borrow, or steal the marvelous secrets they possess. I cannot go alone, for a hundred reasons, therefore I must find a man to accompany me; that man must be one in a thousand, and he must also necessarily be a consummate Chinese scholar. He must be plucky beyond the average, he must be capable of disguising himself so that his nationality shall never for a moment be suspected, and he must go fully convinced in his own mind that he will never return. If he is prepared to undertake so much I am prepared to be generous."

He is convinced that Bruce is the right man for the task. After consideration of the risks and reward, Bruce joins Dr. Nicola on his quest.