brain of the underworld, a brain which might have made or
marred the destiny of nations -- that's the man! But so aloof is he
from general suspicion, so immune from criticism, so admirable
in his management and self-effacement, that for those very words
that you have uttered he could hale you to a court and emerge
with your year's pension as a solatium for his wounded character.
Is he not the celebrated author of The Dynamics of an Asteroid,
a book which ascends to such rarefied heights of pure mathematics
that it is said that there was no man in the scientific
press capable of criticizing it? Is this a man to traduce? Foul-
mouthed doctor and slandered professor -- such would be your
respective roles! That's genius, Watson. But if I am spared by
lesser men, our day will surely come."

"May I be there to see!" I exclaimed devoutly. "But you
were speaking of this man Porlock."

"Ah, yes -- the so-called Porlock is a link in the chain some
little way from its great attachment. Porlock is not quite a sound
link -- between ourselves. He is the only flaw in that chain so far
as I have been able to test it."

"But no chain is stronger than its weakest link."

"Exactly, my dear Watson! Hence the extreme importance of Porlock.
Led on by some rudimentary aspirations towards right, and encouraged
by the judicious stimulation of an occasional ten-pound note sent to
him by devious methods, he has once or twice given me advance
information which has been of value -- that highest value which
anticipates and prevents rather than avenges crime. I cannot doubt
that, if we had the cipher, we should find that this communication
is of the nature that I indicate."

Again Holmes flattened out the paper upon his unused plate. I rose
and, leaning over him, stared down at the curious inscription,
which ran as follows:

         534 C2    13 127 36 31   4  17   21 41

           DOUGLAS 109 293  5  37   BIRLSTONE

             26   BIRLSTONE 9   47     171

"What do you make of it, Holmes?"

"It is obviously an attempt to convey secret information."

"But what is the use of a cipher message without the cipher?"

"In this instance, none at all."

"Why do you say 'in this instance'?"

"Because there are many ciphers which I would read as easily
as I do the apocrypha of the agony column: such crude devices
amuse the intelligence without fatiguing it. But this is different.
It is clearly a reference to the words in a page of some book.
Until I am told which page and which book I am powerless."

"But why 'Douglas' and 'Birlstone'?"

"Clearly because those are words which were not contained in
the page in question."

"Then why has he not indicated the book?"

"Your native shrewdness, my dear Watson, that innate cunning
which is the delight of your friends, would surely prevent
you from inclosing cipher and message in the same envelope.
Should it miscarry, you are undone. As it is, both have to go
wrong before any harm comes from it. Our second post is now
overdue, and I shall be surprised if it does not bring us either a
further letter of explanation, or, as is more probable, the very
volume to which these figures refer."

Holmes's calculation was fulfilled within a very few minutes
by the appearance of Billy, the page, with the very letter which
we were expecting.

"The same writing," remarked Holmes, as he opened the
envelope, "and actually signed," he added in an exultant voice
as he unfolded the epistle. "Come, we are getting on, Watson."
His brow clouded, however, as he glanced over the contents.

"Dear me, this is very disappointing! I fear, Watson, that all
our expectations come to nothing. I trust that the man Porlock
will come to no harm.

 "DEAR MR. HOLMES [he says]:

 "I will go no further in this matter. It is too dangerous -- he

 suspects me. I can see that he suspects me. He came to me

 quite unexpectedly after I had actually addressed this envelope

 with the intention of sending you the key to the cipher.

 I was able to cover it up. If he had seen it, it would have