As we proceeded, the tunnel gradually widened, twisting its way downward at a gentle slope, and after a while the floor became slippery with sea-weed, showing that the tide flowed in at full. In fact, before we had reached the end of the journey we were wading in water up to our knees, for it was still fairly early, about nine or ten, and the tide was only at half ebb. And then my father set his lantern in a niche high up in the wall, and said, "Well, what do you make of it, Tommy?" I looked about me in the dim light, and before me stood a flat wall of rock, split in two, which I recognized at once as the back of the gateway that opened into Ebb-Tide Cave, though whether I should have recognized it so quickly if it hadn't been for my observations of the day before I don't know. I said with something of my father's nonchalance, "This opens into Ebb-Tide Pool." Even my father couldn't quite screen his surprise, for he wasn't to know how I had arrived at my knowledge. "Ha!" he exclaimed, "you're very cute, Tommy." "But look!" I said, and pointed to the twin doors of rock. "But how do you know it opens?" he asked. "I know," I said. "But how?" "It must do," I said doggedly; for I couldn't tell him how I knew. "Yes, it does," he said at length, "but I haven't found out how it's done." We didn't find out that morning either, though we probed every nook and cranny, questing for the secret bolt or spring or whatever it might be which would set that great gate swinging. My father had been over the whole ground before, and I found nothing new to solve the mystery. I thought I had made a discovery when, scrambling up to the niche where my father had set the lantern, I found I could thrust my arm deep into a cranny full of rotting refuse. I cleared it away, but couldn't reach to the end of the little crevice. I pointed it out to my father; but he had explored it before without result. We came away at last, and emerging into the bracken blinked at the blinding daylight. "That's that," said my father, and warned me not to prowl there too often. But I knew what I meant to do. For the rest of the day I reserved my strength, knowing I had been too tired the evening before to do myself justice with the knife; so I lay out on the cliff and bathed in the glorious sun that still beat splendidly from the blue, and before returning I tumbled into the sea for a single plunge, and reached the inn with a magnificent appetite and feeling fit for the evening's encounter. To describe the combat in all its details would take too much space, for it was long and eventful. I tried every artifice my father had taught me, hoping to make my drive without betraying my secret, but he held me in play too surely, and though I managed to parry his attacks I scored no hits myself. As we drew apart for a rest, both panting from the exertion, he asked, "Had enough, Tommy?" And I answered carelessly, "No, I'm fit for another turn," and we closed again.