"Hullo!" he exclaimed. "Look here! Here's a job for Martin Hewitt, after all! Figures! What does that mean? And what an amazing place to put them in! A key barrel! By Jove, Brett, this looks like one of your favourite adventures. Somebody sends a key in an envelope, and a row of incomprehensible figures rolled up inside the key. Look at it!"
I took the key and the paper. The key was of a good sort; small, inscribed "Tripp's Patent" on the bow, and it evidently belonged to a superior lever lock. The paper which had come from the barrel was very thin and tough—a kind I have seen used in typewriters. It had been very carefully and closely rolled, and then pushed into the key so that its natural tendency to open out held it tightly within. Written upon it with a fine pen appeared a series of very minute figures, thus:—
9, 8, 14, 4, 20, 18, 5, 9; 15, 19, 20,
0, 3, 9, 8, 5; 3, 23, 0, 0, 5, 13, 14,
19; 19, 20, 0, 0, 0, 0, 6, 1; 5, 20, 0,
0, 0, 0, 3, 22; 1, 15, 0, 0, 0, 0, 18,
5; 1, 8, 20, 11, 18, 9, 5, 20; 12, 5,
23, 14, 14, 1, 1, 20.
"Well," inquired McCarthy, "what do you make of it?"
"Not much as yet," I admitted. "But it's pretty certain it must be a cryptogram or code-writing of some sort; and if that's the case, I think I might back myself to read it—with a little time." For I well remembered the case of the "Flitterbat Lancers," and the lesson in cypher-reading which Hewitt then gave me.
"Come," my friend replied, much interested, "let's see how you do it. Meantime we'll get on with our lunch."
I took a pencil and a spare sheet of paper, and I studied those figures all through lunch and for some little time after. It soon became plain that the problem was much more difficult than it looked, and I said so. "At the first glance," I said, "it looked a fairly easy cypher; but as a matter of fact, I don't think it's easy at all. One assumes, of course, that the figures stand for letters, and on that assumption two or three peculiarities are noticeable. First, the highest number written here is 23, so that all the letters indicated, in whatever order they may come, are within the compass of the twenty-six letters of the alphabet. Next, the numbers most frequently repeated, if we except the noughts, are 5 and 20, which occur seven times each. Now, the vowel most frequently occurring in average English writing is e, and you will at once perceive that e is number five in the alphabet, counting from the beginning. More, if we go on counting so, we shall find that 20 is t, which is one of the most frequently occurring consonants. This would seem to hint that the cypher is of the very simplest description, consisting of the mere substitution of figures for letters in the exact order of the alphabet. But what, then, of the noughts? What can they mean? More especially when we consider that in three places there are actually four noughts in succession; for, of course, no letter is repeated four times successively in any English word, nor in any foreign word that I can imagine. But let us put down the letters in substitution for the figures, on the supposition that the figures stand for letters in their alphabetical order, leaving the noughts as they are. Then we get this."
I rapidly pencilled the letters on the spare paper, thus:—i, h, n, d, t, r, e, i; o, s, t, 0, c, i, h, e; c, w, 0, 0, e, m, n, s; s, t, 0, 0, 0, 0, f, a; e, t, 0, 0, 0, 0, c, v; a, o, 0, 0, 0, 0, r, e; a, h, t, k, r, i, e, t; l, e, w, n, n, a, a, t.
"See there," I said. "Now, I can make nothing of that. When I come to examine the comparative frequency of the different letters, I find them much as they might be expected to be in a sentence of normal English, and any change would destroy the proportion. E and t are the most frequent, and then come a, n, i, r, s, and c. But as they stand they all mean nothing. It is possible that this may be one of the difficult variable letter cyphers, which Hewitt might read, but I can't. But even then, if the values of the letters change as they would do, they would get out of their normal proportions of frequency; so that a variable letter cypher seems unlikely. And there is another oddity. Look, and you will see that, counting the noughts in, the letters go in groups of eight, with a semi-colon at the end of each group. Now, it is impossible that the message can be a sentence in which every word has exactly eight letters—or, at least, I should think so. It can scarcely be that the semi-colon itself means a letter—it would be singular for one letter to occur with such curious regularity as that. There is no other visible division between the words, nor any single one of the usual aids by which the reader of secret cypher is able to take a hold of his work. No, I'm afraid I must give it up; for the present, at any rate. But I really think it is a thing that would vastly interest Hewitt, if I might show it to him. I suppose I mustn't?"
"Well," McCarthy answered, "perhaps it isn't strictly according to rule, but I think I might venture to lend it to you till to-morrow, if that will do. Indeed, I think, on second thoughts, that I may consider myself quite justified, since it may lead to the man's identification, and it will be a sufficient answer to any inquiry to say that I have shown it to Mr. Martin Hewitt for that purpose. But you'll be careful of it, won't you? Do you want the key, too?"