"The way to use this," he explained, "is to take a keyword—let us say, Darrel. Then let us suppose this message reads, 'The jewels are hidden in ——.' Of course, I'm only supposing this to show you our difficulties. I write the message and place the code word, or keyword above it, thus:
"Dar relDar rel Darrel Da
The jewels are hidden in
"we repeat the keyword over and over as may be necessary. Then we take the first letter, D, and find it in the line across the top of our alphabet square, and the letter under D, which is T we find in the left hand perpendicular line. Now trace the D line down, and the T line across, until the two meet, which gives us W. This would be the first letter of the cipher message if the key word were Darrel, and the message like our suggested one. But the first letter of the cipher we have to solve is O, and no possible amount of guessing can go any further unless we have the key word Mrs. Pell used to guide us. See?"
"Yes, I see," and Miss Darrel nodded her head. "It's most interesting. But, as the first letter of the cipher is O, why can't you find O in your alphabet and go ahead?"
"Because there are twenty-six O's in the square, and it needs the key word to tell which of the twenty-six we want."
"It's perplexing, but I see the plan," and Lucille studied the paper, "however, I doubt if I could make it out, even if I had the word."
"Oh, yes, you could, and if we get the dime and the receipt that was in the pocket-book we can try every word on them both, and I feel sure we'll get the answer. Now, since Pollock, or Young, rather, was so desirous of getting the pin, I argue that he had the necessary key word. Therefore we must get it from him, if we can't get it ourselves, and I doubt if he'll give it up willingly."
"Of course he has the key word," Iris said, "for he told me he could find the jewels and no one else could, if I'd hand over the pin. And he offered to go halves with me! The idea!"
"And yet, if he has the key word, and won't give it up, you can never find the jewels," observed Stone.