(Author’s note: To quote the Tenth Doctor, circa “Blink,” this one got away from me a bit. At one point, I had to stop myself and go “Are you planning to rewrite the entire novel, from the point Watson leaves London to the end?” It looked like a possibility there for a while. I usually try not to make these stories just a redux of the original, but I wanted to use Watson’s being sent off to Dartmoor specifically as a plot point. And then it kind of became “Watson tells me a story for a few thousand words” pretty quickly.
I tried to rein that in a bit. It’s still longer than I intended, and more summary-ish than I wanted, but the basic idea of what I wanted from it is here.)