“Remarkable!” said he.  “Remarkable!”

“You don’t seem surprised.”

“Interested, Mr. Mac, but hardly surprised.  Why should I be surprised?  I receive an anonymous communication from a quarter which I know to be important, warning me that danger threatens a certain person.  Within an hour I learn that this danger has actually materialized and that the person is dead.  I am interested; but, as you observe, I am not surprised.”

In a few short sentences he explained to the inspector the facts about the letter and the cipher.  MacDonald sat with his chin on his hands and his great sandy eyebrows bunched into a yellow tangle.

“I was going down to Birlstone this morning,” said he.  “I had come to ask you if you cared to come with me—­you and your friend here.  But from what you say we might perhaps be doing better work in London.”

“I rather think not,” said Holmes.

“Hang it all, Mr. Holmes!” cried the inspector.  “The papers will be full of the Birlstone mystery in a day or two; but where’s the mystery if there is a man in London who prophesied the crime before ever it occurred?  We have only to lay our hands on that man, and the rest will follow.”

“No doubt, Mr. Mac.  But how do you propose to lay your hands on the so-called Porlock?”

MacDonald turned over the letter which Holmes had handed him.  “Posted in Camberwell—­that doesn’t help us much.  Name, you say, is assumed.  Not much to go on, certainly.  Didn’t you say that you have sent him money?”

“Twice.”

“And how?”

“In notes to Camberwell post office.”

“Did you ever trouble to see who called for them?”

“No.”

The inspector looked surprised and a little shocked.  “Why not?”

“Because I always keep faith.  I had promised when he first wrote that I would not try to trace him.”

“You think there is someone behind him?”

“I know there is.”

“This professor that I’ve heard you mention?”

“Exactly!”

Inspector MacDonald smiled, and his eyelid quivered as he glanced towards me.  “I won’t conceal from you, Mr. Holmes, that we think in the C.I.D. that you have a wee bit of a bee in your bonnet over this professor.  I made some inquiries myself about the matter.  He seems to be a very respectable, learned, and talented sort of man.”

“I’m glad you’ve got so far as to recognize the talent.”

“Man, you can’t but recognize it!  After I heard your view I made it my business to see him.  I had a chat with him on eclipses.  How the talk got that way I canna think; but he had out a reflector lantern and a globe, and made it all clear in a minute.  He lent me a book; but I don’t mind saying that it was a bit above my head, though I had a good Aberdeen upbringing.  He’d have made a grand meenister with his thin face and gray hair and solemn-like way of talking.  When he put his hand on my shoulder as we were parting, it was like a father’s blessing before you go out into the cold, cruel world.”