Caves have always a certain amount of mystery about them, but this one was undoubtedly as ordinary looking a cave as one could find. It did not burrow very far back into the cliff side, and what there was of it was open to the daylight and contained no lurking dark corners. The walls were rough and rocky but not high; the roof was, as Jerry said, nothing particular, and the floor was of shingle and rather wet, as if the sea, now so far away, had paid it a visit not so very long ago. But, as the rocks and stones before the entrance were dry, it was obviously not the tide which had washed the floor. "It must be a spring or something," Hugh said; "let's taste and see--" he stooped as he spoke and scooped up a handful of water, which he put to his lips. "Thought so; it's quite fresh and sweet--that's rather a find--jolly useful for picnics, it will save us carting water about--by jinks!" he exclaimed, looking round at the others with an expression of blank dismay; "do you suppose _that's_ what we were to find to our advantage?" They all stared hard at the shining wet stones, through which the trickle of water was now plainly discernable. Then they stared round the cave again. There did not seem to be a place where treasure _could_ be hidden. Moreover, there were traces of a not very remote picnic--the dead ashes of a gipsy fire, one or two crumpled-up balls of paper, some broken bottles! "That's it," said Jerry at last. "It was probably the people who had that picnic--those broken bottles are the same as the one we found. They played cock-shy with them, and then thought it would be a lark to chuck one into the sea. What a jolly old sell!" "We've had a nice morning anyhow," said Prudence, "and the spring certainly _will_ be an advantage when we've got used to it not being a sewing-machine and bull-dogs and things." "I somehow don't believe it is the spring," said Mollie thoughtfully, still staring about her. "There is something about the way that paper is written; it doesn't look like the writing of the sort of person who plays that kind of joke--and of course it would be meant for a joke. Let's all stand quite still in a circle back to back, and each stare hard all over the bit of cave that comes in front of us, and see if there isn't a sign of some sort." They agreed that there would be no harm in trying this plan, though the boys' hopes were small. Dick and Jerry were uneasily conscious that they were "the sort of person" who would have thought that bottled message an excellent joke--to play on someone else! So they stared. They even circled slowly round so that each part of the cave was examined with meticulous care by six pairs of eyes in turn. But it was all in vain; the cave only seemed to become more and more ordinary the longer they looked at it. "There's not a place where you could hide a thimble," Prue said sadly, "let alone a treasure." "What's that?" Grizzel called out suddenly, pointing to the broken bottles in the corner.