It was while I was sitting moodily in my room one night, debating whether or not to go to bed; weary to exhaustion and yet reluctant to resign myself to a sleep from which I knew I should wake shrieking, that a knock came at the door—­a knock I recognised; and I arose joyfully to admit Godfrey.

I could see by the way his eyes were shining that he had something unusual to tell me; and then, as he looked at me, his face changed.

“What’s the matter, Lester?” he demanded.  “You’re looking fagged out.  Working too hard?”

“It’s not that,” I said.  “I can’t sleep.  This thing has upset my nerves, Godfrey.  I dream about it—­have regular nightmares.”

He sat down opposite me, concern and anxiety in his face.

“That won’t do,” he protested.  “You must go away somewhere—­take a rest, and a good long one.”

“A rest wouldn’t do me any good, as long as this mystery is unsolved,” I said.  “It’s only by working that I can keep my mind off of it.”

“Well,” he smiled, “just to oblige you, we will solve it first, then.”

“Do you mean you know....”

“I know who the Great Unknown is, and I’m going to tell you presently.  Day after to-morrow—­Wednesday—­I’ll know all the rest.  The whole story will be in Thursday morning’s paper.  Suppose you arrange to start Thursday afternoon.”

I could only stare at him.  He smiled as he met my gaze.

“You’re looking better already,” he said, “as though you were taking a little more interest in life,” and he helped himself to a cigar.

“Godfrey,” I protested, “I wish you would pick out somebody else to practise on.  You come up here and explode a bomb just to see how high I’ll jump.  It’s amusing to you, no doubt, and perhaps a little instructive; but my nerves won’t stand it.”

“My dear Lester,” he broke in, “that wasn’t a bomb; that was a simple statement of fact.”

“Are you serious?”

“Perfectly so.”

“But how do you know....”

“Before I answer any questions, I want to ask you one.  Did you, by any chance, mention me to the gentleman known to you as M. Felix Armand?”

“Yes,” I answered, after a moment’s thought; “I believe I did.  I was telling him about our trying to find the secret drawer—­I mentioned your name—­and he asked who you were.  I told him you were a genius at solving mysteries.”

Godfrey nodded.

“That,” he said, “explains the one thing I didn’t understand.  Now go ahead with your questions.”

“You said a while ago that you would know all about this affair day after to-morrow.”

“Yes.”

“How do you know you will?”

“Because I have received a letter which sets the date,” and he took from his pocket a sheet of paper and handed it over to me.  “Read it!”

The letter was written in pencil, in a delicate and somewhat feminine hand, on a sheet of plain, unruled paper.  With an astonishment which increased with every word, I read this extraordinary epistle:—­