THEY set out on the following morning. Elaborate preparations had been made for the undertaking and, so that they might have ample time undisturbed, Doris had begged her mother to allow her to picnic for the day with Sally, and not come back to the hotel for luncheon. As Mrs. Craig had come to have quite a high opinion of Sally, her judgment and knowledge of the river and vicinity, she felt no hesitation in trusting Doris to be safe with her.

Sally had provided the sandwiches and Doris was armed with fruit and candy and books to amuse Genevieve. In the bow of the boat Sally had stowed away a number of tools borrowed from her father’s boathouse. Altogether, the two girls felt as excited and mysterious and adventurous as could well be imagined.

“I wish we could have left Genevieve at home,” whispered Sally as they were embarking. “But there’s no one to take care of her for all day, so of course it was impossible. But I’m afraid she’s going to get awfully tired and restless while we’re working.”

“Oh, never you fear!” Doris encouraged her. “I’ve brought a few new picture-books and we’ll manage to keep her amused somehow.”

Once established in the cave, having settled Genevieve with a book, the girls set to work in earnest.

“I’m glad I thought to bring a dozen more candles,” said Sally. “We were down to the end of the last one. Now shall we begin on that corner at the extreme right-hand away from the door? That’s the likeliest place. I’ll measure a space around it twenty-one inches square.”

She measured off the space on the floor carefully with a folding ruler, while Doris stood over her watching with critical eyes. Then, having drawn the lines with a piece of chalk, Sally proceeded to begin on the sawing operation with one of her father’s old and somewhat rusty saws.

It was a heartbreakingly slow operation. Turn and turn about they worked away, encouraging each other with cheering remarks. The planks of the old Anne Arundel were very thick and astonishingly tough. At the end of an hour they had but one side of the square sawed through, and Genevieve was beginning to grow fractious. Then they planned it that while one worked, the other should amuse the youngest member of the party by talking, singing, and showing pictures to her.

This worked well for a time, and a second side at last was completed. By the time they reached the third, however, Genevieve flatly refused to remain in the cave another moment, so it was agreed that one of them should take her outside while the other remained within and sawed. This proved by far the best solution yet, as Genevieve very shortly fell asleep on the warm pine needles. They covered her with a shawl they had brought, and then both went back to the undertaking, of which they were now, unconfessedly, very weary.

It was shortly after the noon hour when the saw made its way through the fourth side of the square. In a hush of breathless expectation, they lifted the piece of timber, prepared for—who could tell what wondrous secret beneath it?

The space it left was absolutely empty of the slightest suggestion of anything remarkable. It revealed the sandy soil of the embankment into which the cave was dug, and nothing else whatever. The disgusted silence that followed Doris was the first to break.

“Of course, something may be buried down here, but I doubt it awfully. I’m sure we would have seen some sign of it, if this had been the right corner. However, give me that trowel, Sally, and we’ll dig down a way.” She dug for almost a foot into the damp sand, and finally gave it up.

“How could any one go on digging down in the space of only twenty-one inches?” she exclaimed in despair. “If one were to dig at all, the space ought to be much larger. No, this very plainly isn’t the right corner. Let’s go outside and eat our lunch, and then, if we have any courage left, we can come back and begin on another corner. Personally, I feel as if I should scream, if I had to put my hand to that old saw again!”

But a hearty luncheon and a half hour of idling in the sunlight above ground after it, served to restore their courage and determination. Sally was positive that the corner diagonally opposite was the one most likely to yield results, and Doris was inclined to agree with her. Genevieve, however, flatly refused to re-enter the cave so they were forced to adopt the scheme of the morning, one remaining always outdoors with her, as they did not dare let her roam around by herself. Sally volunteered to take the first shift at the sawing, and after they had measured off the twenty-one inch square in the opposite corner she set to work, while Doris stayed outside with Genevieve.

Seated with a picture-book open on her lap, and with Genevieve cuddled close by her side, she was suddenly startled by a muffled, excited cry from within the cave. Obviously, something had happened. Springing up, she hurried inside, Genevieve trailing after her. She beheld Sally standing in the middle of the cave, candle in hand, dishevelled and excited, pointing to the side of the cave near which she had been working.

“Look, look!” she cried. “What did I tell you?” Doris looked, expecting to see something about the floor in the corner to verify their surmises. The sight that met her eyes was as different as possible from that.

A part of the wall of the cave, three feet in width and reaching from top to bottom had opened and swung inward like a door on its hinges.

“What is it?” she breathed in a tone of real awe.

“It’s a door, just as it looks,” explained Sally, “and we never even guessed it was there. I happened to be leaning against that part of the wall as I sawed, balancing myself against it, and sometimes pushing pretty hard. All of a sudden it gave way, and swung out like that, and I almost tumbled in. I was so astonished I hardly knew what had happened!”

“But what’s behind it?” cried Doris, snatching the candle and hurrying forward to investigate. They peered together into the blackness back of the newly revealed door, the candle held high above their heads.

“Why, it’s a tunnel!” exclaimed Sally. “A great, long tunnel, winding away. I can’t even see how far it goes. Did you ever?”

The two girls stood looking at each other and at the opening in a maze of incredulous speculation. Suddenly Sally uttered a satisfied cry.

“I know! I know, now! We never could think where all the rest of the wood from the Anne Arundel went. It’s right here!” It was evidently true. The tunnel had been lined, top and bottom and often at the sides with the same planking that had lined the cave and at intervals there were stout posts supporting the roof of it. Well and solidly had it been constructed in that long ago period, else it would never have remained intact so many years.

“Doris,” said Sally presently, “where do you suppose this leads to?”

“I haven’t the faintest idea,” replied her friend, “except that it probably leads to the treasure or the secret, or whatever it is. That much I’m certain of now.”

“So am I,” agreed Sally, “but, here’s the important thing. Are we to go in there and find it?”

Doris shrank back an instant. “Oh, I don’t know!” she faltered. “I’m not sure whether I dare to—or whether Mother would allow me to—if she knew. It—it might be dangerous. Something might give way and bury us alive.”

“Well, I’ll tell you what I’ll do,” announced Sally courageously. “I’ll take a candle and go in a way by myself and see what it’s like. You stay here with Genevieve, and I’ll keep calling back to you, so you needn’t worry about me.” Before Doris could argue the question with her, she had lighted another candle and stepped bravely into the gloom.

Doris, at the opening, watched her progress nervously, till a turn in the tunnel hid her from sight.

“Oh, Sally, do come back!” she called. “I can’t stand this suspense!”

“I’m all right!” Sally shouted back. “After that turn it goes on straight for the longest way. I can’t see the end. But it’s perfectly safe. The planks are as strong as iron yet. There isn’t a sign of a cave-in. I’m coming back a moment.” She presently reappeared.

“Look here!” she demanded, facing her companion. “Are you game to come with me? We can bring Genevieve along. It’s perfectly safe. If you’re not, you can stay here with her and I’ll go by myself. I’m determined to see the end of this.” Her resolution fired Doris. After all, it could not be so very dangerous, since the tunnel seemed in such good repair. Forgetting all else in her enthusiasm, she hastily consented.

“We must take plenty of candles and matches,” declared Sally. “We wouldn’t want to be left in the dark in there. It’s lucky I brought a lot today. Now, Genevieve, you behave yourself and come along like a good girl, and we’ll buy you some lolly-pops when we get back home!” Genevieve was plainly reluctant to add her presence to the undertaking, but, neither, on the other hand, did she wish to be left behind, so she followed disapprovingly.

Each with a candle lit, they stepped down from the floor of the cave and gingerly progressed along the narrow way. Doris determinedly turned her eyes from the slugs and snails and strange insects that could be seen on the ancient planking, and kept them fastened on Sally’s back as she led the way. On and on they went, silent, awe-stricken, and wondering. Genevieve whimpered and clung to Doris’s skirts, but no one paid any attention to her, so she was forced to follow on, willy-nilly.

So far did this strange, underground passage proceed that Doris half-whispered: “Is it never going to end, Sally? Ought we to venture any further?”

“I’m going to the end!” announced Sally stubbornly. “You can go back if you like.” And they all went on again in silence.

At length it was evident that the end was in sight, for the way was suddenly blocked by a stone wall, apparently, directly across the passage. They all drew a long breath and approached to examine it more closely. It was unmistakably a wall of stones, cemented like the foundation of a house, and beyond it they could not proceed.

“What are we going to do now?” demanded Doris.

“The treasure must be here,” said Sally, “and I’ve found one thing that opened when you pushed against it. Maybe this is another. Let’s try. Perhaps it’s behind one of these stones. Look! The plaster seems to be loose around these in the middle.” She thrust the weight of her strong young arm against it, directing it at the middle stone of three large ones, but without avail. They never moved the fraction of an inch. Then she began to push all along the sides where the plaster seemed loose. At last she threw her whole weight against it—and was rewarded!

The three stones swung round, as on a pivot, revealing a space only large enough to crawl through with considerable squeezing.

“Hurrah! hurrah!” she shouted. “What did I tell you, Doris? There’s something else behind here,—another cave, I guess. I’m going through. Are you going to follow?” Handing her candle to Doris, she scrambled through the narrow opening. And Doris, now determined to stick at nothing, set both candles on the ground, and pushed the struggling and resisting Genevieve in next. After that, she passed in the candles to Sally, who held them while she clambered in herself.

And, once safely within, they stood and stared about them.

“Why, Sally,” suddenly breathed Doris, “this isn’t a cave. It’s a cellar! Don’t you see all the household things lying around? Garden tools, and vegetables and—and all that? Where in the world can we be?” A great light suddenly dawned on her.

“Sally Carter, what did I tell you? This cellar is Miss Camilla’s. I know it. I’m certain of it. There’s no other house anywhere near Slipper Point. I told you she knew about that cave!”

Sally listened, open-mouthed. “It can’t be,” she faltered. “I’m sure we didn’t come in that direction at all.”

“You can’t tell how you’re going—underground,” retorted Doris. “Remember, the tunnel made a turn, too. Oh, Sally! Let’s go back at once, before anything is discovered, and never, never let Miss Camilla or any one know what we’ve discovered. It’s none of our business.”

Sally, now convinced, was about to assent, when Genevieve suddenly broke into a loud howl.

“I won’t go back! I won’t go back—in that nas’y place!” she announced, at the top of her lungs.

“Oh, stop her!” whispered Doris. “Do stop

her, or Miss Camilla may hear!” Sally stifled her resisting sister by the simple process of placing her hand forcibly over her mouth,—but it was too late. A door opened at the top of a flight of steps, and Miss Camilla’s astounded face appeared in the opening.

“What is it? Who is it?” she called, obviously frightened to death herself at this unprecedented intrusion. Huddled in a corner, they all shrank back for a moment, then Doris stepped boldly forward.

“It’s only ourselves, Miss Camilla,” she announced. “We have done a very dreadful thing, and we hadn’t any right to do it. But, if you’ll let us come upstairs, we’ll explain it all, and beg your pardon, and promise never to speak of it or even think of it again.” She led the others up the cellar steps, and into Miss Camilla’s tiny, tidy kitchen. Here, still standing, she explained the whole situation to that lady, who was still too overcome with astonishment to utter a word. And she ended her explanation thus:

“So you see, we didn’t have the slightest idea we were going to end at this house. But, all the same, we sort of felt that this cave was a secret of yours and that we really hadn’t any right to be interfering with it. But won’t you please forgive us, this time, Miss Camilla? And we’ll really try to forget that it ever existed.”

And then Miss Camilla suddenly found words. “My dear children,” she stuttered, “I—I really don’t know what you’re talking about. I haven’t the faintest idea what this all means. I never knew till this minute that there was anything like a cave or a tunnel connected with this house!”

And in the astounded silence that followed, the three stood gaping, open-mouthed, at each other.