Sherlock Holmes had many secrets. This is the greatest of them. Our knowledge of the life and career of Mr Sherlock Holmes is necessarily partial and inexact. Riddled with lacunae and ambiguities, its parameters are defined chiefly by what his friend and colleague, Dr John Watson, saw fit to record. One era in particular – those enigmatic years in which, believed dead at the Reichenbach Falls, the Great Detective roved the world incognito – has been shrouded in obscurity and doubt, the particulars of that time too terrible and too strange to be set down in full. At least, that is, until now...