This fourth novel of Boothby's Dr. Nikola series reveals that Nikola has discovered all of the facts necessary to extend a human being's life. He has studied science and magic secrets of Tibetan monks. He explains: "It has been a long and tedious search, but such labour only makes success the sweeter. The machinery is now prepared; all that remains is to fit the various parts together. In six months' time, if all goes well, I will have a man walking upon this earth who, under certain conditions, shall live a thousand years."

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.

In this the third of Boothby's Dr. Nikola novels, Nikola applies his almost hypnotic persuasion to convince an out-of-luck Australian, formerly from England, named Gilbert Pennethorne to assist Nikola unwittingly in an evil scheme. Nikola takes advantage of Pennethorne's intense desire for revenge against a former boss in Australia who stole information about the location of a gold field that would have made Pennethorne immensely wealthy.

This is the first in Boothby's series of Dr. Nikola novels. It opens with the manager of a fine London restaurant preparing for a dinner reserved in an odd letter originating from Brazil 3 months prior, for 4 persons in a private room, where 3 guests will arrive showing cards with a red dot. One will be from China, one from South Africa, one from England, plus the host, Dr Nikola, who is of unknown nationality but is later revealed to travel the world widely.

This is the last of Boothby's Dr. Nikola novels, set in Venice, Italy. Nikola tells the story of his sad life, demonstrates his mystic ability to enable people to experience themselves in another place and time, transforms a man into being a beast, and departs from his palace in Venice which has a bloody history, but he remains in the minds of those who met him.