In this alternate-world Sherlock Holmes story, Holmes is accompanied by Dr Theodore Moriarty, and Irish occultist and Freemason, It uses aspects of Moriarty's real career, including a period spent at Mossel Bay in South Africa.
Moriarty (an historical figure) is not connected to Holmes' nemesis of the same surname, but the story does play with the connection. He is also the subject of fictional stories by his mentee Dion Fortune (who wrote about him as the character Dr Taverner).
