“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 gone hard with me. But I read suspicion in his eyes. Please burn the cipher message, which can now be of no use to you.