at the inner plate, which contains the keyhole. Look at the thousands of scratches all round the hole—marks where the key has slipped. What sober man’s key could have scored those grooves? But you will never see a drunkard’s watch without them. He winds it at night, and he leaves these traces of his unsteady hand. Where is the mystery in all this?”

“It is as clear as daylight,” I answered. “I regret the injustice which I did you. I should have had more faith in your marvellous faculty. May I ask whether you have any professional inquiry on foot at present?”

“None. Hence the cocaine. I cannot live without brainwork. What else is there to live for? Stand at the window here. Was ever such a dreary, dismal, unprofitable world? See how the yellow fog swirls down the street and drifts across the dun-coloured houses. What could be more hopelessly prosaic and material? What is the use of having powers, Doctor, when one has no field upon which to exert them? Crime is commonplace, existence is commonplace, and no qualities save those which are commonplace have any function upon earth.”

I had opened my mouth to reply to this tirade when, with a crisp knock, our landlady entered, bearing a card upon the brass salver.

“A young lady for you, sir,” she said, addressing my companion.

“Miss Mary Morstan,” he read. “Hum! I have no recollection of the name. Ask the young lady to step up, Mrs. Hudson. Don’t go, Doctor. I should prefer that you remain.”