"Whew! It's like climbing down the ladder of a lighthouse," exclaimed Dulcie, subsiding on to a convenient stone. Her legs were shaking in a most unaccountable fashion, and her breath coming and going far more rapidly than was comfortable. "It might have been worse," affirmed Deirdre, trying not to show that her nerve had in any degree failed her, and surveying the scene with the eye of a prospector. They were in a small and very narrow cove, so hidden between cliffs which jutted out overhead that it was practically invisible from above, and certainly could not be seen from anywhere in the school grounds. It was a pretty little creek, with a silvery slip of beach, and green clumps of ferns growing high up in the interstices of the rocks; quite a romantic spot, so beautiful and secluded that it might almost be the haunt of a mermaiden or a water nixie. The ferns, which were flourishing in unusual luxuriance, caught Deirdre's attention. "I believe it's the sea-spleenwort," she remarked. "Don't you remember we found some at Kergoff, and Miss Birks was so excited about it? I'm sure she doesn't know all this is growing at the very bottom of her own garden. I'll try and get a root." To obtain a root was more easily said than done, however. Most of the clumps of fern were in very inaccessible situations, and too deeply embedded in the rock to be removed. Deirdre climbed from one to another in vain, then noticing a particularly fine group of fronds on a projecting shelf far above her head, commenced to scale the cliff. She reached the shelf fairly easily, but instead of setting to work to try to uproot the fern, she gave a long whistle of surprise. "What's the matter?" asked Dulcie from below. "Matter! Come up yourself and see! Oh, goody!" Dulcie was still a little shaky, but spurred on by curiosity she got up the cliff somehow, and added a "Hallo!" of amazement to her chum's exclamations. Facing them was the entrance to a cave. At one time it had evidently been carefully blocked up, but now the wooden boarding that guarded it had been wrenched asunder, leaving a small opening just sufficient to enter by. The girls peeped cautiously in, but beyond the first few yards all was dark. This was indeed a discovery. The mouth of the cave was so effectually hidden by the crags which surrounded it that nobody would have suspected its existence who had not come across it by accident. What secrets lay in its mysterious depths, who could say? Thrilled with excitement, the girls turned to one another. "If we could only explore it!" breathed Dulcie. "We're going to!" returned Deirdre firmly. "I shall run back this instant to the house for a candle. You wait here."