At Slipper Point, they established Genevieve, as uusal, on the old chair in the cave, to examine by candle-light the new picture-book that Doris had brought for her. This was calculated to keep her quiet for a long while, as she was inordinately fond of "picters," as she called them.
"Now," cried Sally, "what about that paper?"
"Oh, I don't know that it amounts to very much," explained Doris. "It just occurred to me, in looking it over, that possibly the fact of its being square and the little cave also being square might have something to do with things. Suppose the floor of the cave were divided into squares just as this paper is. Now do you notice one thing? Read the letters in their order up from the extreme left hand corner diagonally. It reads r-i-g-h-t-s and the last square is blank. Now why could n't that mean 'right' and the 's' stand for square, - the 'right square' being that blank one in the extreme corner?"
"Goody!" cried Sally. "That 's awfully clever of you. I never thought of such a thing as reading it that way, in all the time I had it. And do you think that perhaps the treasure is buried under there?"
"Well, of course, that 's all we can think it means. It might be well to investigate in that corner."
But another thought had occurred to Sally. "If that 's so," she inquired dubiously, "what 's the use of all the rest of those letters and numbers. They must be there for something."
"They may be just a 'blind,' and mean nothing at all," answered Doris. "You see they 'd have to fill up the spaces somehow, or else, if I 'm right, they 'd have more than one vacant square. And one was all they wanted. So they filled up the rest with a lot of letters and figures just to puzzle any one that got hold of it. But there 's something else I 've thought of about it. You notice that the two outside lines of squares that lead up to the empty squares are just numbers, - not letters at all. Now I 've added each line together and find that the sum of each side is exactly twenty-one. Why would n't it be possible that it means the sides of this empty square are twenty-one - something - in length. It can't possibly mean twenty-one feet because the whole cave is only about nine feet square. It must mean twenty-one inches."
Sally was quite overcome with amazement at this elaborate system of reasoning it out. "You certainly are a wonder!" she exclaimed. "I never would have thought of it in the world."
"Why, it was simple," declared Doris, "for just as soon as I 'd hit upon that first idea, the rest all followed like clockwork. But now, if all this is right, and the treasure lies somewhere under the vacant square, our business is to find it."
Suddenly an awful thought occurred to Sally. "But how are going to know which corner that square is in? It might be any of the four, might n't it?"
For a moment Doris was stumped. How, indeed, were they going to tell? Then one solution dawned on her. "Would n't they have been most likely to consider the square of the floor as it faces you, coming in at the door, to be the way that corresponds to the plan on the paper? In that case, the extreme right-hand corner from the door, for the space of twenty-one inches, is the spot."
It certainly seemed the most logical conclusion. They rushed over to the spot and examined it, robbing Genevieve of her candle in order to have the most light on the dark corner. It exhibited, however, no signs of anything the least unusual about it. The rough planks of the flooring joined quite closely to those of the wall, and there was no evidence of its having ever been used as a place of concealment. At this discouraging revelation, their faces fell.
"Let 's examine the other corners," suggested Doris. "Perhaps we 're not right about this being the one."
The others, however, revealed no difference in their appearance, and the girls restored her candle to Genevieve at the table, and stood gazing at each other in disconcerted silence.
"But, after all," suggested Doris shortly, "would you expect to see any real sign of the boards being movable or having been moved at some time? That would only give their secret away, when you come to think of it. No, if there is some way of opening one of those corners, it 's pretty carefully concealed, and I don't see anything for it but for us to bring some tools up here, - a hammer and saw and chisel, perhaps, - and go to work prying those boards up." The plan appealed to Sally.
"I 'll get some of Dad's," she declared. "He 's got a lot of tools in the boathouse, and he 'd never miss a few of the older ones. We 'll bring them up tomorrow and begin. And I think your first idea about the corner was the best. We 'll start over there."
"I 's cold," Genevieve began to whimper, at this point. "I don't like it in here. I want to go out."
The two girls laughed. "She is n't much of a treasure-hunter, is she!" said Doris. "Bless her heart. We 'll go out right away and sit down under the pine trees."
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