Ever since A. C. Black & Co. brought out their first Whos Who? of the great and good in 1849 (followed in 1897 by Who Was Who after death intervened and removed their entries to a separate volume) people have been fascinated by the rich and famous. So there is, for example, a Whos Who in cricket, a Whos Who in Agatha Christie. And even a Whos Who in a famous cemetery.
So if you have ever wanted to know where Watson bought his boots, or where (and when) Inspectors Lestrade, Bradstreet, Athelney Jones, Hopkins and MacDonald appear in the stories then this is the book for you. How many times is Moriarty mentioned, and what was his henchman, Colonel Moran, up to in an empty house? Who on earth was Acton and, more to the point, who could possibly have been called (by the Great Detective himself) a rival to Sherlock Holmes?