“I’d like to hear.”

“Six thousand a year.  That’s paying for brains, you see—­the American business principle.  I learned that detail quite by chance.  It’s more than the Prime Minister gets.  That gives you an idea of Moriarty’s gains and of the scale on which he works.  Another point:  I made it my business to hunt down some of Moriarty’s checks lately—­just common innocent checks that he pays his household bills with.  They were drawn on six different banks.  Does that make any impression on your mind?”

“Queer, certainly!  But what do you gather from it?”

“That he wanted no gossip about his wealth.  No single man should know what he had.  I have no doubt that he has twenty banking accounts; the bulk of his fortune abroad in the Deutsche Bank or the Credit Lyonnais as likely as not.  Sometime when you have a year or two to spare I commend to you the study of Professor Moriarty.”

Inspector MacDonald had grown steadily more impressed as the conversation proceeded.  He had lost himself in his interest.  Now his practical Scotch intelligence brought him back with a snap to the matter in hand.

“He can keep, anyhow,” said he.  “You’ve got us side-tracked with your interesting anecdotes, Mr. Holmes.  What really counts is your remark that there is some connection between the professor and the crime.  That you get from the warning received through the man Porlock.  Can we for our present practical needs get any further than that?”

“We may form some conception as to the motives of the crime.  It is, as I gather from your original remarks, an inexplicable, or at least an unexplained, murder.  Now, presuming that the source of the crime is as we suspect it to be, there might be two different motives.  In the first place, I may tell you that Moriarty rules with a rod of iron over his people.  His discipline is tremendous.  There is only one punishment in his code.  It is death.  Now we might suppose that this murdered man—­this Douglas whose approaching fate was known by one of the arch-criminal’s subordinates—­had in some way betrayed the chief.  His punishment followed, and would be known to all—­if only to put the fear of death into them.”

“Well, that is one suggestion, Mr. Holmes.”

“The other is that it has been engineered by Moriarty in the ordinary course of business.  Was there any robbery?”

“I have not heard.”

“If so, it would, of course, be against the first hypothesis and in favour of the second.  Moriarty may have been engaged to engineer it on a promise of part spoils, or he may have been paid so much down to manage it.  Either is possible.  But whichever it may be, or if it is some third combination, it is down at Birlstone that we must seek the solution.  I know our man too well to suppose that he has left anything up here which may lead us to him.”

“Then to Birlstone we must go!” cried MacDonald, jumping from his chair.  “My word! it’s later than I thought.  I can give you, gentlemen, five minutes for preparation, and that is all.”