“Yes,” the old expert responded. “But I suppose no one has ever discovered the key to the cipher?”
“No. Lost centuries ago, I expect.”
“Unless that document of Knutton’s contains it,” I remarked to my friend.
“Ah!” he gasped. “I never thought of that! This may be the absolute record with the plan, and the Knutton parchment the key to the cipher.”
“If so, then we’ve lost it! We are too late,” I remarked, my heart sinking.
“Professor Campbell, of Edinburgh, was much interested in it, and tried to make it out two years ago, but utterly failed,” was the assistant-keeper’s remark, and a few moments later, after we had handed the roll back to the attendant, he left us, and I returned with Staffurth to his house in Clapham.
Well versed as Staffurth was in the art of cryptic writing as practised during the fifteenth and sixteenth centuries, he utterly failed to decipher what I had copied. The signatures alone were in plain script—all the rest in cipher.
I took a copy of the document for myself, and through nearly a fortnight spent my leisure in trying, with the aid of the key in the vellum book, to decipher the first line, all, however, in vain. The cryptogram was a complicated one in any case. Staffurth consulted two men he knew who were experts in such things, but both gave it up as a private cipher that could not be read without a key.
One night, however, while lying in bed reflecting, as all of us do when our minds are troubled, that oft-repeated numerical three suddenly occurred to me. Could it be possible that it was the key to the cipher? This idea became impressed upon me, so I rose and, going into my sitting-room, lit my lamp, and there and then commenced to work upon it.
After several trials in taking three as the key-number, I at last made the experiment of taking C for A, and so on, writing the third letter from the one required. The alphabet I wrote then read as follows —