at his back, there are infinite possibilities. Anyhow, Friend
Porlock is evidently scared out of his senses--kindly compare the
writing in the note to that upon its envelope; which was done, he
tells us, before this ill-omened visit. The one is clear and
firm. The other hardly legible."

"Why did he write at all? Why did he not simply drop it?"

"Because he feared I would make some inquiry after him in that
case, and possibly bring trouble on him."

"No doubt," said I. "Of course." I had picked up the original
cipher message and was bending my brows over it. "It's pretty
maddening to think that an important secret may lie here on this
slip of paper, and that it is beyond human power to penetrate
it."

Sherlock Holmes had pushed away his untasted breakfast and lit
the unsavoury pipe which was the companion of his deepest
meditations. "I wonder!" said he, leaning back and staring at
the ceiling. "Perhaps there are points which have escaped your
Machiavellian intellect. Let us consider the problem in the
light of pure reason. This man's reference is to a book. That
is our point of departure."

"A somewhat vague one."

"Let us see then if we can narrow it down. As I focus my mind
upon it, it seems rather less impenetrable. What indications
have we as to this book?"