One of the comforts of the Arthur Conan Doyle stories is their almost staid adherence to form. Villains and cases come and go up the staircase at 221B Baker Street, but within that refuge, life stays the same: Holmes all-knowing and calm, Watson fretful and frightened, clues orderly, victims distraught, never a problem not seemingly insoluble. Outside is the fabled Victorian London, a city we all know in our imaginations.