On visiting Reginald Musgrave, a friend of Holmes' from university, an ancient ritual leads to the disappearance of Brunton, the butler. Sherlock Holmes, with the help of Dr Watson, discovers the origins of the ritual and tries to uncover the butler's secret and the mystery of the long lost crown of King Charles I.
Tom Quinn has disappeared, having been accused of assassinating the Chief of the Defence Staff. Could this be the perfect opportunity for conspirators in the darker corners of government to overhaul MI5, or is there still time to prove Tom's innocence?
