“I do not understand you, Kah!” said Newton sharply. “Is the body of my friend in this buried place? What happened? Speak more clearly.”

“No, I have talked too much of forbidden things.” Kah raised up his spear.

“Go now! Go — for I have no wish to slay!”

“You cannot slay, Kah, for your spears will not fly this far. And the great one called Grag will be as a wall against your coming.”

Rapidly, under his breath, Newton spoke to the robot. “Keep them back, Grag! They can’t harm you, and it’ll leave us free to dig.”

Clanking ponderously down the slope, a terrifying gigantic form in the dusk, Grag advanced on the Vulcanians. And Newton cried aloud to Kah, “We will not leave this place until we have found our friend!”

Kah flung his spear. It fell short by no more than two paces but Newton did not stir. The Vulcanian drew back slowly before the oncoming Grag, who spread out his mighty arms and roared and made the ground tremble under his feet.

“The big ham!” whispered Otho. “He’s enjoying it.”

There was a wavering among the ranks of the natives. A ragged flight of spears pelted up the slope and some of the obsidian points splintered with a sharp ringing sound on Grag’s metallic body. Grag laughed a booming laugh. He picked up a slab of stone and broke it in his hands and flung the pieces at them.

“That does it”, said Otho disgustedly. “I’m going to be sick.”

Kah screamed suddenly, “The curse will fall on you as it fell on the other who entered there! You too will go out along the Beam, lost forever from the sight of men!”

He turned then and vanished into the jungle.

“I have been studying this landslide”, said Simon Wright irrelevantly. “I believe that it was artificially caused by the natives to seal this place after Carlin entered it.”

“Very likely”, Captain Future answered. He stood for a moment in deep though. “I wonder what Kah meant by the ‘Bright Ones who do not return’?”

“Probably an euphemism for the dead”, said Otho pessimistically. “We’ll know better when we’ve found a way inside.”

They turned to and began to dig again. The citadel stood on a sort of promontory, partly blocked now by the slide, so that the natives could only come at them up the slope, and Grag effectively barred the way. Now and again a spear whistled harmlessly into the dirt but there was no attack.

The last glowing thread of the Beam narrowed into nothingness and was gone. Utter darkness descended on the hidden world of Vulcan. Newton and Otho worked on by the light of belt-lamps.

They struck the solid stone of the building, and the work went faster. After a few minutes Otho cried, “There’s an opening here!”

They discarded their improvised spades. The loose dirt flew under their hands and presently they had uncovered the upper arches of a triple window. From there the way was easy.

Curt Newton was the first one inside. A great quantity of dirt had poured in through the open arches but most of this upper level was clear. Otho slid agilely after him, and then the Brain.

The lamps showed them a circular gallery, high up in the central cupola. Below was a round and empty shaft. Newton leaned out over the low carved railing. Far down in the pit he could see a soft and curdled luminescence, like spectral sunlight veiled in mist. The source was hidden from him by the overhang of other galleries lower down.

The silence of age-long death was in the place and the mingled smell of centuries and of the raw new soil. Newton led the way around the gallery, his footsteps ringing hollow against the vault of stone.

He found a narrow stairway, going down.

They descended, passing the other galleries, and came at last into a small chamber. It had had a door to the outside, a massive, age-tarnished metal door that had buckled somewhat with pressure and had let dirt sift through the cracks.

Opposite the door was a low, square opening in the stone wall. Above it was an inscription. Holding his lamp high, Curt Newton read slowly, “Here is the birthplace of the Children of the Sun.”

WONDERINGLY they went through into the central chamber of the citadel. Dirt had spilled down from above, covering a good part of the floor. Newton realized that only the upper gallery, serving as a stop for the soil to dam itself against, had saved the interior of the citadel from being heavily inundated.

He scrambled up onto that heap of rock and soil, and then stood still, gazing in puzzled wonder. He saw now the sources of that dim, eerie light. Set in deep niches on opposite faces of the curving wall were two seeming identical sets of apparatus, like nothing he had ever seen before.

The bases were of some dark metal, untouched by the passage of time. They were wide and low, separated so that their centers formed a dais. Each base bore two soaring coils of what seemed to be crystal tubing, as high as a tall man, braced in frames of platinum.

The coils pulsed and glowed with misty light — one set giving forth a gleam of purest gold, the other a darker hue of bluish green. Opposite the arch through which they had entered was a third niche, much smaller, having within it a complicated bank of instruments that might have been a control panel.

“Birthplace of the Children of the Sun”, said Otho softly. “Look, Curt — there above the niches.”

Again Captain Future read aloud, the warning messages cut deep in the ageless stone. Above the apparatus of the golden coils it said, “Let him beware who steps beyond this portal. For death is the price of eternal life!”

Above the one of somber hue, the inscription read “Death is a double doorway. On which side of it is the true life?”

Simon Wright had approached the niche that held the strange glow of sunlight and was hovering over the edge of the fallen soil there. “Curtis”, he said, “I think we have found what we sought.”

Newton joined him. He bent and picked something up, shaking it free from the dirt that half buried it. Mutely he nodded and showed the thing to Otho. It was a coverall of tough synthetic cloth, much stained and worn. On the label inside the collar was woven the name, Philip Carlin.

“He was here then, Otho. “But what happened to him? Why would he strip — wait!”

The android’s sharp eyes had perceived a mound in the soil, vaguely manlike in shape. Together he and Newton uncovered it and then looked at each other in vast relief.

“It’s only his knapsack and bedroll”, said Newton thankfully.

“And his boots.” Otho shook his head “I don’t get it at all. There’s no sign of blood on his clothes —”

Newton was looking now at the yel— crystal coils, the suggestive dais-like space between them. The thing was close to him, almost close enough to touch.

“He stripped here”, said Newton slowly. “He left his clothing and his kit behind and —” His eyes lifted to the inscription and he added very softly, “Phil Carlin went through the portal, whatever it is and wherever it leads.”

“I agree with your assumptions, Curtis”, said Simon Wright. “I suggest that you search Carlin’s effects for any data he may have left relative to this apparatus and its uses. It is obvious that he spent months in study and such a record seems inevitable.”

Simon’s lens-eyes turned toward the small niche with the cryptic bank of controls.

“See, there are many close-packed inscriptions on those walls, presumably instructions for the operation of these machines. He would surely have written down his translations for reference.”

Captain Future was already going through Carlin’s pack. “Here it is!” he said and held up a thick notebook. “Hold your light closer, Otho.”

He thumbed rapidly through the pages until he found what he was hoping and praying for — a section headed, in Carlin’s meticulous script, Translation of Formulae, Control Niche.