Up from that machine, if machine it was, soared the black basalt wall of that end of the cavern. But there above the gray mechanism the rough wall had been carved with a great, smooth facet, a giant, gleaming black oval face as smooth as though planed and polished. Only, at the middle of the glistening black oval face, were carven deeply four large and wholly unfamiliar characters. As Ennis and Campbell stared frozenly across the awe-inspiring place, sound swelled from the hundreds of throats. A slow, rising chant, it climbed and climbed until the basalt roof above seemed to quiver to it, crashing out with stupendous effect, a weird litany in an unknown tongue. Then it began to fall.

Ennis clutched the inspector's gray-robed arm. "Where's Ruth?" he whispered frantically. "I don't see any prisoners."

"They must be somewhere here," Campbell said swiftly. "Listen----"

As the chant died to silence, on the dais at the farther end of the cavern the hooded man who wore the triple-jeweled star stepped forward and spoke. His deep, heavy voice rolled out and echoed across the cavern, flung back and forth from wall to rocky wall.

"Brothers of the Door," he said, "we meet again here in the Cavern of the Door this year, as for ten thousand years past our forefathers have met here to worship They Beyond the Door, and bring them the sacrifices They love.

"A hundred centuries have gone by since first They Beyond the Door sent their wisdom through the barrier between their universe and ours, a barrier which even They could not open from their side, but which their wisdom taught our fathers how to open.

"Each year since then have we opened the Door which They taught us how to build. Each year we have brought them sacrifices. And in return They have given us of their wisdom and power. They have taught us things that lie hidden from other men, and They have given us powers that other men have not.

"Now again comes the time appointed for the opening of the Door. In their universe on the other side of it, They are waiting now to take the sacrifices which we have procured for them. The hour strikes, so let the sacrifices be brought."

As though at a signal, from a small opening at one side of the cavern a triple file of marchers entered. A file of hooded gray members of the Brotherhood flanked on either side a line of men and women who did not wear the hoods or robes. They were thirty or forty in number. These men and women were of almost all races and cla.s.ses, but all of them walked stiffly, mechanically, staring ahead with unseeing, distended eyes, like living corpses.

"Drugged!" came Campbell's shaken voice. "They're all drugged, and don't know what is going on."

Ennis' eyes fastened on a small, slender girl with chestnut hair who walked at the end of the line, a girl in a straight tan dress, whose face was white, stiff, like those of the others.

"There's Ruth!" he exclaimed frantically, his cry m.u.f.fled by his hood.

He plunged in that direction, but Campbell held him back.

"No!" rasped the inspector. "You can't help her by simply getting yourself captured!"

"I can at least go with her!" Ennis exclaimed. "Let me go!"

Inspector Campbell's iron grip held him. "Wait, Ennis!" said the detective. "You've no chance that way. That robe of Chandra Da.s.s' you're wearing has a double-star badge like those of the men up there on the dais. That means that as Chandra Da.s.s you're ent.i.tled to be up there with them. Go up there and take your place as though you were Chandra Da.s.s--with the hood on, they can't tell the difference. I'll slip around to that side door out of which they brought the prisoners. It must connect with the tunnels, and it's not far from the dais. When I fire my pistol from there, you grab your wife and try to get to that door with her. If you can do it, we'll have a chance to get up through the tunnels and escape."

Ennis wrung the inspector's hand. Then, without further reply, he walked boldly with measured steps up the main aisle of the cavern, through the gray ranks to the dais. He stepped up onto it, his heart racing. The chief priest, he of the triple-star, gave him only a glance, as of annoyance at his lateness. Ennis saw Campbell's gray figure slipping round to the side door.

The gray-hooded hundreds before him had paid no attention to either of them. Their attention was utterly, eagerly, fixed upon the stiff-moving prisoners now being marched up onto the dais. Ennis saw Ruth pa.s.s him, her white face an unfamiliar, staring mask.

The prisoners were ranged at the back of the dais, just beneath the great, gleaming black oval facet. The guards stepped back from them, and they remained standing stiffly there. Ennis edged a little toward Ruth, who stood at the end of that line of stiff figures. As he moved imperceptibly closer to her, he saw the two priests beside the gray mechanism reaching toward knurled k.n.o.bs of ebonite affixed to its side, beneath the spherical web of pulsing wires.

The chief priest, at the front of the dais, raised his hands. His voice rolled out, heavy, commanding, reverberating again through all the cavern.

_5. The Door Opens_

"Where leads the Door?" rolled the chief priest's voice.

Back up to him came the reply of hundreds of voices, m.u.f.fled by the hoods but loud, echoing to the roof of the cavern in a thunderous response.

"_It leads outside our world!_"

The chief priest waited until the echoes died before his deep voice rolled on in the ritual.

"Who taught our forefathers to open the Door?"

Ennis, edging desperately closer and closer to the line of victims, felt the mighty response reverberate about him.

"_They Beyond the Door taught them!_"

Now Ennis was apart from the other priests on the dais, within a few yards of the captives, of the small figure of Ruth.

"To whom do we bring these sacrifices?"

As the high priest uttered the words, and before the booming answer came, a hand grasped Ennis and pulled him back from the line of victims.

He spun round to find that it was one of the other priests who had jerked him back.

"_We bring them to Those Beyond the Door!_"

As the colossal response thundered, the priest who had jerked Ennis back whispered urgently to him. "You go too close to the victims, Chandra Da.s.s! Do you wish to be taken with them?"

The fellow had a tight grip on Ennis' arm. Desperate, tensed, Ennis heard the chief priest roll forth the last of the ritual.

"Shall the Door be opened that They may take the sacrifices?"

Stunning, mighty, a tremendous shout that mingled in it worshipping awe and superhuman dread, the answer crashed back.

_"Let the Door be opened!"_

The chief priest turned and his up-flung arms whirled in a signal.

Ennis, tensing to spring toward Ruth, saw the two priests at the gray mechanism swiftly turn the knurled black k.n.o.bs. Then Ennis, like all else in the vast cavern, was held frozen and spellbound by what followed.

The spherical web of wires pulsed up madly with shining force. And up at the center of the gleaming black oval facet on the wall, there appeared a spark of unearthly green light. It blossomed outward, expanded, an awful viridescent flower blooming quickly outward farther and farther.

And as it expanded, Ennis saw that he could look _through_ that green light! He looked through into another universe, a universe lying infinitely far across alien dimensions from our own, yet one that could be reached through this door between dimensions. It was a green universe, flooded with an awful green light that was somehow more akin to darkness than to light, a throbbing, baleful luminescence.

Ennis saw dimly through green-lit s.p.a.ces a city in the near distance, an unholy city of emerald hue whose unsymmetrical, twisted towers and minarets aspired into heavens of h.e.l.lish viridity. The towers of that city swayed to and fro and writhed in the air. And Ennis saw that here and there in the soft green substance of that restless city were circles of lurid light that were like yellow eyes.

In ghastly, soul-shaking apprehension of the utterly alien, Ennis knew that the yellow circles were _eyes_--that that h.e.l.l-sp.a.w.ned city of another universe was _living_--that its unfamiliar life was single yet multiple, that its lurid eyes looked now through the Door!

Out from the insane living metropolis glided pseudopods of its green substance, glided toward the Door. Ennis saw that in the end of each pseudopod was one of the lurid eyes. He saw those eyed pseudopods come questing through the Door, onto the dais.

The yellow eyes of light seemed fixed on the row of stiff victims, and the pseudopods glided toward them. Through the open door was beating wave on wave of unfamiliar, tingling forces that Ennis felt even through the protective robe.

The hooded mult.i.tude bent in awe as the green pseudopods glided toward the victims faster, with avid eagerness. Ennis saw them reaching for the prisoners, for Ruth, and he made a tremendous mental effort to break the spell that froze him. In that moment pistol-shots crashed across the cavern and a stream of bullets smashed the pulsing web of wires!

The Door began instantly to close. Darkness crept back around the edges of the mighty oval. As though alarmed, the lurid-eyed pseudopods of that h.e.l.l-city recoiled from the victims, back through the dwindling Door.

And as the Door dwindled, the light in the cavern was failing.

"Ruth!" yelled Ennis madly, and sprang forward and grasped her, his pistol leaping into his other hand.