Arthur Hall 
Demon of the Dusk [PDF ebook] 
The Rediscovered Cases of Sherlock Holmes Book 1

Sherlock Holmes and Doctor Watson are summoned to Theobald Grange, the Warwickshire home of Lady Heminworth. Being of a nervous and superstitious disposition, her Ladyship lives in fear. Her husband and elder son were recently murdered, apparently by the ghost of a court jester who was executed on the site centuries before. The apparition has warned that she, too, is to die. Holmes rejects a supernatural explanation, although his adversary seems unaffected by gunfire and is able to take flight and disappear. The Great Detective brings his powers to bear, but still the killings continue…