Sir Arthur claimed to have had conversations with the spirits of many great men, including Cecil Rhodes, Earl Haig, Joseph Conrad and others. Adrian Conan Doyle, the novelist’s son, said today the whole family believed Sir Arthur would continue to keep in touch with them.
“I know perfectly well I am going to have conversations with my father,” he said. [source]
There are two other areas of interest to which Doyle is linked.
Doyle has been linked to the Piltdown Man hoax. This linkage is not anything close to certain, and actually reads like a typical conspiracy novel. For instance, one of the reasons why no one has made this link before, according to the authors of this idea, is because the evidence was, and continues to be, so elusive…. (read about it here).
The other area of interest, and much more viable as a jumping off point, is the link made by Eco and Sebeok between the inferential processes bestowed upon Holmes by his creator Doyle and the semiotic theory of C.S. Peirce. This is explored in the book: The Sign of Three: Dupin, Holmes, Peirce (Advances in Semiotics).
(Dupin is, of course, Poe’s detective.)