A Lost Clue
"Suppose we admit, for the sake of argument," began Betty "that John Thaneford was in possession of the secret. Then everything points back to his father, old Fielding, who certainly had all the brains of the family. Last and most important, it was a secret which Mr. Thaneford, senior, desired to impart to me; he did tell me all he could."
"The series of numbers, you mean? I recall them perfectly: 1-4-2-4-8. And what then?"
"Do you remember the story of Christian and his fellow pilgrim, Hopeful, imprisoned in Giant Despair's stronghold of Doubting Castle? After languishing for a week or more in darkness and misery, Hopeful suddenly bethinks him of a key which he has in his bosom, a key that will unlock any door in the castle. The rest is easy.
"So, too, I had my key, but I had only used it once—to unlock the first and most obvious door——"
"The combination of the safe," I interrupted.
"Precisely. It never occurred to either of us that it might be a master-key to which all locks must yield. But so it was.
"Not that I learned to use it without a lot of trouble and discouragement. It took months and months, and I only got it fully working on the train trip down from Stockbridge.
"Of course, you have guessed that the whole story lay buried in that leather-bound book belonging to Fielding Thaneford which we found in the safe. I remembered all that you had told me about 'Le Chiffre Indéchiffrable,' but even granting that that particular cypher had been employed, how was I ever to stumble upon the indispensable key-word, or more likely, key-sentence?
"One day I had an inspiration. There was the series of numbers: 1-4-2-4-8. Considered as numbers merely they could be of no use, since most cypher codes are built up on letters. But I might put the numbers into their written word equivalents, thus: One-four-two-four-eight It was certainly conceivable that these letters might form the key-sentence; it would be all the more easily memorized since, in its numerical form, it served as a combination to the safe.