I find it recorded in my pocket book that it was on the night of May the Tenth, 1896, when the stairwell adjoining our Baker Street apartments was filled with the clatter of someone’s hurried approach. Holmes, who had hitherto been sunk into one of his absorbed periods of bleak introspection  — so much so, I confess, that I had half expected him to reach for the seven percent solution — roused himself enough to comment: “I wonder, Watson, what could bring a denizen of Boston to our rooms at this time of the night?”

He waved away my perplexed protests with an airy explication: “Come, come, Watson. You must know that I have written a monograph on the subject of the clogs of East America. Their tenor is as unmistakeable as the sound of your wheezing cough in the October fogs. But, stay, our visitor is upon us!”

Holmes threw open the door to…