“Well?” Mr. Sabin interjected.

“I notice that Duson was found in your sitting-room.  It occurs to me as a possibility that he may have met with a fate intended for some one else—­for yourself, for instance, sir!”

“But I,” Mr. Sabin said smoothly, “am a member of no secret society, nor am I conscious of having enemies sufficiently venomous to desire my life.”

The detective sat for a moment with immovable face.

“We, all of us, know our friends, sir,” he said.  “There are few of us properly acquainted with our enemies.”

Mr. Sabin lit a cigarette.  His fingers were quite steady, but this man was making him think.

“You do not seriously believe,” he asked, “that Duson met with a death which was intended for me?”

“I am afraid,” the detective said thoughtfully, “that I know no more about it than you do.”

“I see,” Mr. Sabin said, “that I am no stranger to you.”

“You are very far from being that, sir,” the man answered.  “A few years ago I was working for the Government—­and you were not often out of my sight.”

Mr. Sabin smiled.

“It was perhaps judicious,” he remarked, “though I am afraid it proved of very little profit to you.  And what about the present time?”

“I see no harm in telling you, sir, that a general watch is kept upon your movements.  Duson was useful to us ... but now Duson is dead.”

“It is a fact,” Mr. Sabin said impressively, “that Duson was a genius.  My admiration for him continually increases.”

“Duson made harmless reports to us as we desired them,” the detective said.  “I have an idea, however, that if this course had at any time been inimical to your interests that Duson would have deceived us.”

“I am convinced of it,” Mr. Sabin declared.

“And Duson is dead!”

Mr. Sabin nodded gravely.

The little hard-visaged man looked steadily for a moment upon the carpet.

“Duson died virtually whilst accepting pay from if not actually in the employ of our Secret Service Department.  You will understand, therefore, that we, knowing of this complication in his life, naturally incline towards the theory of murder.  Shall I be taking a liberty, sir, if I give you an unprofessional word of warning?”

Mr. Sabin raised his eyebrows.

“By no means,” he answered.  “But surely you cannot—­”

The man smiled.

“No, sir,” he said drily.  “I do not for one moment suspect you.  The man was our spy upon your movements, but I am perfectly aware that there has been nothing worth reporting, and I also know that you would never run such a risk for the removal of so insignificant a person.  No, my warning comes to you from a different point of view.  It is, if you will pardon my saying so, none the less personal, but wholly friendly.  The case of Duson will be sifted to the dregs, but unless I am greatly mistaken, and I do not see room for the possibility of a mistake, I know the truth already.”