“Well, the name has a familiar sound. Someone in a novel, was he not? I don’t take much stock of detectives in novels—chaps that do things and never let you see how they do them. That’s just inspiration: not business.”

“Jonathan Wild wasn’t a detective, and he wasn’t in a novel. He was a master criminal, and he lived last century—1750 or thereabouts.”

“Then he’s no use to me. I’m a practical man.”

“Mr. Mac, the most practical thing that you ever did in your life would be to shut yourself up for three months and read twelve hours a day at the annals of crime. Everything comes in circles—even Professor Moriarty. Jonathan Wild was the hidden force of the London criminals, to whom he sold his brains and his organization on a fifteen per cent. commission. The old wheel turns, and the same spoke comes up. It’s all been done before, and will be again. I’ll tell you one or two things about Moriarty which may interest you.”

“You’ll interest me, right enough.”

“I happen to know who is the first link in his chain—a chain with this Napoleon-gone-wrong at one end, and a hundred broken fighting men, pickpockets, blackmailers, and card sharpers at the other, with every sort of crime in between. His chief of staff is Colonel Sebastian Moran, as aloof and guarded and inaccessible to the law as himself. What do you think he pays him?”

“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 Crédit 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?”