The Secret Journals of Sherlock Holmes — June Thomson

SECRETS, SUSPENSE, AND CONSPIRACY. LONDON THROUGH THE EYES OF THE GREAT SHERLOCK HOLMES
As Dr Watson's old manuscripts, deliberately unpublished to protect the names of those they concern, are released into the public, a multitude of previously unseen cases are revealed.
An American millionaire receives threatening letters from a sinister Black Hand . . . A mysterious box terrifies a shop keeper . . . Holmes and Watson feel the influence of an old enemy from beyond the grave . . . And a tragedy occurs which Sherlock Holmes will never be able to forgive himself for failing to prevent.
With murders, madness and diamonds abound, June Thomson continues the Holmes canon with a brilliance and ingenuity that perfectly captures where Conan Doyle left off.