“Of course, I was prepared to find Dr. Watson,” he remarked with a courteous bow. “His collaboration may be very necessary, for we are dealing on this occasion, Mr. Holmes, with a man to whom violence is familiar and who will, literally, stick at nothing. I should say that there is no more dangerous man in Europe.”

“I have had several opponents to whom that flattering term has been applied,” said Holmes with a smile. “Don’t you smoke? Then you will excuse me if I light my pipe. If your man is more dangerous than the late Professor Moriarty, or than the living Colonel Sebastian Moran, then he is indeed worth meeting. May I ask his name?”

“Have you ever heard of Baron Gruner?”

“You mean the Austrian murderer?”

Colonel Damery threw up his kid-gloved hands with a laugh. “There is no getting past you, Mr. Holmes! Wonderful! So you have already sized him up as a murderer?”

“It is my business to follow the details of Continental crime. Who could possibly have read what happened at Prague and have any doubts as to the man’s guilt! It was a purely technical legal point and the suspicious death of a witness that saved him! I am as sure that he killed his wife when the socalled ‘accident’ happened in the Splugen Pass as if I had seen him do it. I knew, also, that he had come to England and had a presentiment that sooner or later he would find me some work to do. Well, what has Baron Gruner been up to? I presume it is not this old tragedy which has come up again?”

“No, it is more serious than that. To revenge crime is important, but to prevent it is more so. It is a terrible thing, Mr. Holmes, to see a dreadful event, an atrocious situation, preparing itself before your eyes, to clearly understand whither it will lead and yet to be utterly unable to avert it. Can a human being be placed in a more trying position?”

“Perhaps not.”

“Then you will sympathize with the client in whose interests I am acting.”

“I did not understand that you were merely an intermediary. Who is the principal?”

“Mr. Holmes, I must beg you not to press that question. It is important that I should be able to assure him that his honoured name has been in no way dragged into the matter. His motives are, to the last degree, honourable and chivalrous, but he prefers to remain unknown. I need not say that your fees will be assured and that you will be given a perfectly free hand. Surely the actual name of your client is immaterial?”

“I am sorry,” said Holmes. “I am accustomed to have mystery at one end of my cases, but to have it at both ends is too confusing. I fear, Sir James, that I must decline to act.”

Our visitor was greatly disturbed. His large, sensitive face was darkened with emotion and disappointment.

“You hardly realize the effect of your own action, Mr. Holmes,” said he. “You place me in a most serious dilemma for I am perfectly certain that you would be proud to take over the case if I could give you the facts, and yet a promise forbids me from revealing them all. May I, at least, lay all that I can before you?”