“Put into plain words, the matter is this,” said he. “In your opinion there is a diabolical agency which makes Dartmoor an unsafe abode for a Baskerville - that is your opinion?”

“At least I might go the length of saying that there is some evidence that this may be so.”

“Exactly. But surely, if your supernatural theory be correct, it could work the young man evil in London as easily as in Devonshire. A devil with merely local powers like a parish vestry would be too inconceivable a thing.”

“You put the matter more flippantly, Mr. Holmes, than you would probably do if you were brought into personal contact with these things. Your advice, then, as I understand it, is that the young man will be as safe in Devonshire as in London. He comes in fifty minutes. What would you recommend?”

“I recommend, sir, that you take a cab, call off your spaniel who is scratching at my front door, and proceed to Waterloo to meet Sir Henry Baskerville.”

“And then?”

“And then you will say nothing to him at all until I have made up my mind about the matter.”

“How long will it take you to make up your mind?”

“Twenty-four hours. At ten o’clock to-morrow, Dr. Mortimer, I will be much obliged to you if you will call upon me here, and it will be of help to me in my plans for the future if you will bring Sir Henry Baskerville with you.”

“I will do so, Mr. Holmes.” He scribbled the appointment on his shirt-cuff and hurried off in his strange, peering, absent-minded fashion. Holmes stopped him at the head of the stair.

“Only one more question, Dr. Mortimer. You say that before Sir Charles Baskerville’s death several people saw this apparition upon the moor?”

“Three people did.”

“Did any see it after?”

“I have not heard of any.”

“Thank you. Good-morning.”

Holmes returned to his seat with that quiet look of inward satisfaction which meant that he had a congenial task before him.

“Going out, Watson?”

“Unless I can help you.”

“No, my dear fellow, it is at the hour of action that I turn to you for aid. But this is splendid, really unique from some points of view. When you pass Bradley’s, would you ask him to send up a pound of the strongest shag tobacco? Thank you. It would be as well if you could make it convenient not to return before evening. Then I should be very glad to compare impressions as to this most interesting problem which has been submitted to us this morning.”

I knew that seclusion and solitude were very necessary for my friend in those hours of intense mental concentration during which he weighed every particle of evidence, constructed alternative theories, balanced one against the other, and made up his mind as to which points were essential and which immaterial. I therefore spent the day at my club and did not return to Baker Street until evening. It was nearly nine o’clock when I found myself in the sitting-room once more.

My first impression as I opened the door was that a fire had broken out, for the room was so filled with smoke that the light of the lamp upon the table was blurred by it. As I entered, however, my fears were set at rest, for it was the acrid fumes of strong coarse tobacco which took me by the throat and set me coughing. Through the haze I had a vague vision of Holmes in his dressing-gown coiled up in an armchair with his black clay pipe between his lips. Several rolls of paper lay around him.

“Caught cold, Watson?” said he.

“No, it’s this poisonous atmosphere.”

“I suppose it is pretty thick, now that you mention it.”

“Thick! It is intolerable.”

“Open the window, then! You have been at your club all day, I perceive.”

“My dear Holmes!”

“Am I right?”