In fog-enshrouded Victorian London, Sherlock Holmes and Doctor Watson soon become entangled in a deadly web of intrigue and cryptic clues.
Who is the silver-caned shadowy stranger? Is Euclid's College lecturer John Kindred really in danger? And what is the connection to the fabled and priceless emerald, the Egyptian Sepulchre?
Holmes slowly suspects that the answers may lie behind a quite extraordinary equation.