My friend was telling me about this theory or something the other day that explains how a bunch of literary characters are all part of some sort of group, society, family, order, or something like that. It’s not really something that’s explicit in the books, but more of a unifying theory that somehow ties together a bunch of disparate characters.
He referred to it as a “sort of League of Extraordinary Gentlemen” concept, but involving 19th-cen literature. I think he said that Sherlock Holmes was a member of the group.
It’s more of a game than a theory, really (not to mention ripe fanfic territory). Some of the better essays have been compiled into a book.
(Some more distant relatives on the extensive Holmes family tree: Nigel Townsend of Crossing Jordan, and Robert Goren of Law and Order: Criminal Intent.