In honourable homage to Conan Doyle, Caleb Carr escorts Holmes and Watson through what transpires to be one of their most sensational adventures - one of their 'largely secret sub-collection' of cases, swathed in discretion and bound by decorum. Rightly so, given the delicate nature of the investigation: murder in a royal palace, an affront to the majesty of Queen Victoria, and a tantalising take on another, ancient murder. One witnessed by the wilful Mary Queen of Scots...