"Yes," Watson says, breathless. "The very same. Or he did, until... well. I lived there too, before I married." And then he forges ahead, because it's incredibly important to work out what is and is not the same right now. "We met in 1881 when I was invalided out of the army. We worked together for a good ten years."

And then, hesitant, because if the answer is yes it may very well be upsetting, "Does the name 'Moriarty' mean anything to you?"