"What next?" asked Larry.

"I think we ought to take a look around," I replied in the same low tones. "We'll climb the wall here and take a flash about. The whole place ought to be plain as day from that height."

Huldricksson, his blue eyes alert, nodded. With the greatest difficulty we clambered up the broken blocks.

To the east and south of us, set like children's blocks in the midst of the sapphire sea, lay dozens of islets, none of them covering more than two square miles of surface; each of them a perfect square or oblong within its protecting walls.

On none was there sign of life, save for a few great birds that hovered here and there, and gulls dipping in the blue waves beyond.

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 a.n.a.lysis 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 pa.s.sed. 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 pa.s.s 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 pa.s.sed 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.

"It's the door?" he asked. I nodded. There was a low whistle from him and he pointed up toward the top of the grey stone. I followed the gesture and saw, above the moon door and on each side of it, two gently curving bosses of rock, perhaps a foot in diameter.

"The moon door's keys," I said.

"It begins to look so," answered Larry. "If we can find them," he added.

"There's nothing we can do till moonrise," I replied. "And we've none too much time to prepare as it is. Come!"

A little later we were beside our boat. We lightered it, set up the tent, and as it was now but a short hour to sundown I bade them leave me and make their search. They went off together, and I busied myself with opening some of the paraphernalia I had brought with me.

First of all I took out the two Becquerel ray-condensers that I had bought in Sydney. Their lenses would collect and intensify to the fullest extent any light directed upon them. I had found them most useful in making spectroscopic a.n.a.lysis of luminous vapours, and I knew that at Yerkes Observatory splendid results had been obtained from them in collecting the diffused radiance of the nebulae for the same purpose.

If my theory of the grey slab's mechanism were correct, it was practically certain that with the satellite only a few nights past the full we could concentrate enough light on the bosses to open the rock.

And as the ray streams through the seven globes described by Throckmartin would be too weak to energize the Pool, we could enter the chamber free from any fear of encountering its tenant, make our preliminary observations and go forth before the moon had dropped so far that the concentration in the condensers would fall below that necessary to keep the portal from closing.

I took out also a small spectroscope, and a few other instruments for the a.n.a.lysis of certain light manifestations and the testing of metal and liquid. Finally, I put aside my emergency medical kit.

I had hardly finished examining and adjusting these before O'Keefe and Huldricksson returned. They reported signs of a camp at least ten days old beside the northern wall of the outer court, but beyond that no evidence of others beyond ourselves on Nan-Tauach.

We prepared supper, ate and talked a little, but for the most part were silent. Even Larry's high spirits were not in evidence; half a dozen times I saw him take out his automatic and look it over. He was more thoughtful than I had ever seen him. Once he went into the tent, rummaged about a bit and brought out another revolver which, he said, he had got from Da Costa, and a half-dozen clips of cartridges. He pa.s.sed the gun over to Olaf.

At last a glow in the southeast heralded the rising moon. I picked up my instruments and the medical kit; Larry and Olaf shouldered each a short ladder that was part of my equipment, and, with our electric flashes pointing the way, walked up the great stairs, through the enclosures, and straight to the grey stone.

By this time the moon had risen and its clipped light shone full upon the slab. I saw faint gleams pa.s.s over it as of fleeting phosph.o.r.escence--but so faint were they that I could not be sure of the truth of my observation.

We set the ladders in place. Olaf I a.s.signed to stand before the door and watch for the first signs of its opening--if open it should. The Becquerels were set within three-inch tripods, whose feet I had equipped with vacuum rings to enable them to hold fast to the rock.

I scaled one ladder and fastened a condenser over the boss; descended; sent Larry up to watch it, and, ascending the second ladder, rapidly fixed the other in its place. Then, with O'Keefe watchful on his perch, I on mine, and Olaf's eyes fixed upon the moon door, we began our vigil. Suddenly there was an exclamation from Larry.

"Seven little lights are beginning to glow on this stone!" he cried.

But I had already seen those beneath my lens begin to gleam out with a silvery l.u.s.tre. Swiftly the rays within the condenser began to thicken and increase, and as they did so the seven small circles waxed like stars growing out of the dusk, and with a queer--curdled is the best word I can find to define it--radiance entirely strange to me.

Beneath me I heard a faint, sighing murmur and then the voice of Huldricksson:

"It opens--the stone turns--"

I began to climb down the ladder. Again came Olaf's voice:

"The stone--it is open--" And then a shriek, a wail of blended anguish and pity, of rage and despair--and the sound of swift footsteps racing through the wall beneath me!

I dropped to the ground. The moon door was wide open, and through it I caught a glimpse of a corridor filled with a faint, pearly vaporous light like earliest misty dawn. But of Olaf I could see--nothing! And even as I stood, gaping, from behind me came the sharp crack of a rifle; the gla.s.s of the condenser at Larry's side flew into fragments; he dropped swiftly to the ground, the automatic in his hand flashed once, twice, into the darkness.

And the moon door began to pivot slowly, slowly back into its place!

I rushed toward the turning stone with the wild idea of holding it open. As I thrust my hands against it there came at my back a snarl and an oath and Larry staggered under the impact of a body that had flung itself straight at his throat. He reeled at the lip of the shallow cup at the base of the slab, slipped upon its polished curve, fell and rolled with that which had attacked him, kicking and writhing, straight through the narrowing portal into the pa.s.sage!

Forgetting all else, I sprang to his aid. As I leaped I felt the closing edge of the moon door graze my side. Then, as Larry raised a fist, brought it down upon the temple of the man who had grappled with him and rose from the twitching body unsteadily to his feet, I heard shuddering past me a mournful whisper; spun about as though some giant's hand had whirled me--

The end of the corridor no longer opened out into the moonlit square of ruined Nan-Tauach. It was barred by a solid ma.s.s of glimmering stone. The moon door had closed!

O'Keefe took a stumbling step toward the barrier behind us. There was no mark of juncture with the shining walls; the slab fitted into the sides as closely as a mosaic.

"It's shut all right," said Larry. "But if there's a way in, there's a way out. Anyway, Doc, we're right in the pew we've been heading for--so why worry?" He grinned at me cheerfully. The man on the floor groaned, and he dropped to his knees beside him.

"Marakinoff!" he cried.

At my exclamation he moved aside, turning the face so I could see it.

It was clearly Russian, and just as clearly its possessor was one of unusual force and intellect.

The strong, ma.s.sive brow with orbital ridge unusually developed, the dominant, high-bridged nose, the straight lips with their more than suggestion of latent cruelty, and the strong lines of the jaw beneath a black, pointed beard all gave evidence that here was a personality beyond the ordinary.

"Couldn't be anybody else," said Larry, breaking in on my thoughts.

"He must have been watching us over there from Chau-ta-leur's vault all the time."

Swiftly he ran practised hands over his body; then stood erect, holding out to me two wicked-looking magazine pistols and a knife. "He got one of my bullets through his right forearm, too," he said. "Just a flesh wound, but it made him drop his rifle. Some a.r.s.enal, our little Russian scientist, what?"

I opened my medical kit. The wound was a slight one, and Larry stood looking on as I bandaged it.

"Got another one of those condensers?" he asked, suddenly. "And do you suppose Olaf will know enough to use it?"