“It’s not an airy nothing, you see,” said he, smiling. “On the contrary, it is solid enough for a man to break his hand over. Is Mrs. Watson in?”

“She is away upon a visit.”

“Indeed! You are alone?”

“Quite.”

“Then it makes it the easier for me to propose that you should come away with me for a week to the Continent.”

“Where?”

“Oh, anywhere. It’s all the same to me.”

There was something very strange in all this. It was not Holmes’s nature to take an aimless holiday, and something about his pale, worn face told me that his nerves were at their highest tension. He saw the question in my eyes, and, putting his finger-tips together and his elbows upon his knees, he explained the situation.

“You have probably never heard of Professor Moriarty?” said he.

“Never.”

“Ay, there’s the genius and the wonder of the thing!” he cried. “The man pervades London, and no one has heard of him. That’s what puts him on a pinnacle in the records of crime. I tell you Watson, in all seriousness, that if I could beat that man, if I could free society of him, I should feel that my own career had reached its summit, and I should be prepared to turn to some more placid line in life. Between ourselves, the recent cases in which I have been of assistance to the royal family of Scandinavia, and to the French republic, have left me in such a position that I could continue to live in the quiet fashion which is most congenial to me, and to concentrate my attention upon my chemical researches. But I could not rest, Watson, I could not sit quiet in my chair, if I thought that such a man as Professor Moriarty were walking the streets of London unchallenged.”

“What has he done, then?”

“His career has been an extraordinary one. He is a man of good birth and excellent education, endowed by nature with a phenomenal mathematical faculty. At the age of twenty-one he wrote a treatise upon the binomial theorem, which has had a European vogue. On the strength of it he won the mathematical chair at one of our smaller universities, and had, to all appearances, a most brilliant career before him. But the man had hereditary tendencies of the most diabolical kind. A criminal strain ran in his blood, which, instead of being modified, was increased and rendered infinitely more dangerous by his extraordinary mental powers. Dark rumours gathered round him in the university town, and eventually he was compelled to resign his chair and to come down to London, where he set up as an army coach. So much is known to the world, but what I am telling you now is what I have myself discovered.

“As you are aware, Watson, there is no one who knows the higher criminal world of London so well as I do. For years past I have continually been conscious of some power behind the malefactor, some deep organizing power which forever stands in the way of the law, and throws its shield over the wrong-doer. Again and again in cases of the most varying sorts - forgery cases, robberies, murders - I have felt the presence of this force, and I have deduced its action in many of those undiscovered crimes in which I have not been personally consulted. For years I have endeavoured to break through the veil which shrouded it, and at last the time came when I seized my thread and followed it, until it led me, after a thousand cunning windings, to ex-Professor Moriarty, of mathematical celebrity.