“That’s a part of the mystery,” said Doris. “And her brother’s mixed up in it somehow, and perhaps her father. That much I’m sure of. She talks freely enough about everything else except those things, so that must be it. Do you know what I’m almost tempted to think? That her brother did commit some crime, and her father hid him away in the cave to escape from justice, but she couldn’t have known about it, that’s plain. Because she did not know about the cave and tunnel at all till just lately. Perhaps she wondered what became of him. And maybe they sold all her lovely porcelains to make up for what he’d done somehow.”
“Yes,” cried Sally in sudden excitement. “And another idea has just come to me. Maybe that queer paper was a note her brother left for her and she can’t make out how to read it. Did you ever think of that?”
“Why, no!” exclaimed Doris, struck with the new idea. “I never thought of it as anything he might have left for her. Do you remember, she said once they were awfully fond of each other, more even than most brothers and sisters? It would be perfectly natural if he did want to leave her a note, if he had to go away and perhaps never come back. And of course he wouldn’t want any one else to understand what it said. Oh, wait!—I have an idea we’ve never thought of before. Why on earth have we been so stupid!—”
She sprang up and began to walk about excitedly, while Sally watched her, consumed with curiosity. At length she could bear the suspense no longer.
“Well, for pity’s sake tell me what you’ve thought of!” she demanded. “I’ll go wild if you keep it to yourself much longer.”
“Where’s that copy?” was all Doris would reply. “I want to study it a moment.” Sally drew it from her pocket and handed it to her, and Doris spent another five minutes regarding it absorbedly.
“It is. It surely is!” she muttered, half to herself. “But how are we ever going to think out how to work it?” At last she turned to the impatient Sally.
“I’m a fool not to have thought of this before, Sally. I read a book once,—I can’t think what it was now, but it was some detective story,—where there was something just a little like this. Not that it looked like this, but the idea was the same. If it is what I think, it isn’t the note itself at all. The note, if there is one, must be somewhere else. This is only a secret code, or arrangement of the letters, so that one can read the note by it. Probably the real note is written in such a way that it could never be understood at all without this. Do you understand?”
Sally had indeed grasped the idea and was wildly excited by it.
“Oh, Doris,” she cried admiringly. “You certainly are a wonder to have thought all this out! It’s ten times as interesting as what we first thought it was. But how do you work this code? I can’t make anything out of it at all.”