We turned our gaze down upon the island on which we stood. It was, I estimated, about three-quarters of a mile square. The sea wall enclosed it. It was really an enormous basalt-sided open cube, and within it two other open cubes. The enclosure between the first and second wall was stone paved, with here and there a broken pillar and long stone benches. The hibiscus, the aloe tree, and a number of small shrubs had found place, but seemed only to intensify its stark loneliness. "Wonder where the Russian can be?" asked Larry. I shook my head. There was no sign of life here. Had Marakinoff gone--or had the Dweller taken him, too? Whatever had happened, there was no trace of him below us or on any of the islets within our range of vision. We scrambled down the side of the gateway. Olaf looked at me wistfully. "We start the search now, Olaf," I said. "And first, O'Keefe, let us see whether the grey stone is really here. After that we will set up camp, and while I unpack, you and Olaf search the island. It won't take long." Larry gave a look at his service automatic and grinned. "Lead on, Macduff," he said. We made our way up the steps, through the outer enclosures and into the central square, I confess to a fire of scientific curiosity and eagerness tinged with a dread that O'Keefe's analysis might be true. Would we find the moving slab and, if so, would it be as Throckmartin had described? If so, then even Larry would have to admit that here was something that theories of gases and luminous emanations would not explain; and the first test of the whole amazing story would be passed. But if not--And there before us, the faintest tinge of grey setting it apart from its neighbouring blocks of basalt, was the moon door! There was no mistaking it. This was, in very deed, the portal through which Throckmartin had seen pass that gloriously dreadful apparition he called the Dweller. At its base was the curious, seemingly polished cup-like depression within which, my lost friend had told me, the opening door swung. What was that portal--more enigmatic than was ever sphinx? And what lay beyond it? What did that smooth stone, whose wan deadness whispered of ages-old corridors of time opening out into alien, unimaginable vistas, hide? It had cost the world of science Throckmartin's great brain--as it had cost Throckmartin those he loved. It had drawn me to it in search of Throckmartin--and its shadow had fallen upon the soul of Olaf the Norseman; and upon what thousands upon thousands more I wondered, since the brains that had conceived it had vanished with their secret knowledge? What lay beyond it? I stretched out a shaking hand and touched the surface of the slab. A faint thrill passed through my hand and arm, oddly unfamiliar and as oddly unpleasant; as of electric contact holding the very essence of cold. O'Keefe, watching, imitated my action. As his fingers rested on the stone his face filled with astonishment.