he metal plate that had sealed him in this tomb fell open with a crash. Beyond it the passageway was alive with crowding red figures. Above their heads the nozzles of a score of flame-throwers spat jets of green fire. Rawson drew back in sudden uncontrollable horror as they came crowding into the room.

The familiar feel of the bailer's cold metal had given him a momentary sense of oneness with his own world. Now this inrush of hideous, demoniac figures beneath the flare of green flames was like a fevered vision of the infernal regions come suddenly to actuality.

Rawson retreated to the shattered, rocky wall and prepared for one last fight, until he realized that the evil black eyes in their ghastly circles of white skin were fixed upon him more in curiosity than in active hatred.

They formed a semicircle about him—a wall of red bodies, whose pointed heads were craned forward, while an excited chatter in their broken, whistling speech filled the room with shrill clamor. Then one of them pointed above toward the open shaft that Rawson had drilled, the shaft up which the bailer had gone. And again their voices rose in weird discord, while their long arms waved, and red, lean-fingered hands pointed.

Only a moment of this, then one of them gave an order. Two of the red figures came toward Rawson where he was waiting. They were unarmed. They motioned that he was to go with them. And Dean, with a helpless shrug of his shoulders, allowed them, one on each side, to take him by the arms and hurry him through the open door. Two others went ahead, the green jets of flame from their weapons lighting the passage.

The system of communicating tunnels seemed at first only the vents and blow-holes from some previous volcanic activity. And yet, at times they gave place to more regular arrangement that plainly was artificial. The air in them was pure, though odorous with a pungent tang which Dean could not identify. Through some of the passages it blew gently with uncomfortable warmth.

The guard of wild red figures hurried him along through a vast world of caverns and winding passages which seemed one great mine. The richness of it was amazing. Dean Rawson was a man, a human being, facing death in some form which he could not yet know, and, so fast had his wild experiences crowded in upon him, he seemed numbed to all normal emotions; yet through it all the mind of the engineer was at work, and Dean's eyes were flashing from side to side, trying to see and understand the ever-changing panorama of a subterranean world.

ole-men, both red and yellow, were everywhere. But it was apparent at a glance that the yellow giants were a race of toilers—slaves, driven by the reds.

Their great bodies glowed orange-colored with the reflected heat of the blasts of flame used to melt the metals from their ores. Gold and silver, other metals that Rawson could not distinguish in the half light—the glow of the molten stuff came from every distant cave that the passages opened up.

The sheer marvel of it overwhelmed him. His own danger, even the death that waited for him, were forgotten.

A world within a world—and who knew how far it extended? Mole-men, by scores and hundreds, the denizens of a great subterranean world, of which his own world had been in ignorance. Here was civilization of a sort, and now the barriers that had separated this world from the world above had been broken down; the two were united. Suddenly there came to Rawson's mind a flashing comprehension of a menace wild and terrible that had come with the breaking of those barriers.

They were passing through a wider hall when the whistling chatter of Dean's escort ceased. They were looking to one side where a cloud of smoke had rolled from a slope beyond. One of the red figures staggered, choking, from the cloud. Two yellow mole-men followed closely after.

The red mole-man was unarmed; each yellow one had a flame-thrower that was now so familiar a sight to Dean. His own escort was silent; they had halted, watching those others expectantly.

n the silence of that rocky room the single red one whistled an order. One of the two yellow men placed his weapon on the floor. Another shrill order followed, and the remaining worker, without a moment's hesitation, turned the green blast of his own projector upon his comrade.

It was done in a second—a second in which the giant's shriek ended in a flash of flame for which his own flesh was the fuel. A wisp of drifting smoke, and that was all. And the red creatures who had Rawson in their charge, after a moment of silence, filled the room with shrill-voiced pandemonium, while they shrieked their approval of the spectacle.

But Dean Rawson's lips were forming half-whispered words, so intently was he thinking the thoughts. "The damned red beast! That poor devil's flame hit some sulphur, I suppose—burned it to SO_2—then he got his!"

But, even while he searched his mind for words to describe the evil of this red race, he was realizing another fact. These yellow giants, countless thousands of them, perhaps, were held in subjection by their red masters. They would do as they were told. Dimly, vaguely, through his horrified mind, came the picture of a horde of red and yellow beasts turned loose upon the world above.

There were fears now which filled Dean Rawson, shook him with horrors as yet only half comprehended. But the fears were not for himself, one solitary man in the grip of these red beasts—he was fearing for all mankind.

is guard was hurrying him on, but now Dean hardly saw the scenes of feverish activity through which they passed. Another thought had come to him.

That shaft, the hole which he himself had drilled—what damage had it done? It was he who had broken down the barriers. His drill had told these beasts that there was other life above. It had guided them. They had realized that they were near to some other place where men worked and drove tunnels through the rocks. They had followed up these forgotten passages that led to the old craters, had ascended inside the volcano, made their way through the top and emerged into another world—a clean and sunlit world.

Now Rawson's eyes found with new understanding the activity about him.

The mining operations had been left behind. Here were branching passages, great cavelike rooms—a world within a world, in all truth. Throughout it, demoniac figures were hurrying, driving thousands of giant yellow slaves where the light shone sparkling from innumerable heaps of metal weapons—flame-throwers and others, the nature of which Rawson could not determine. And everywhere was the shouting and hurry as of a nation in the throes of war.

His speculations ended abruptly. They were approaching a room, a vast open place. High on the farther wall was a recess in the rock in which tongues of flame licked hungrily upward. The heat of the fires struck down in a ceaseless hot blast. Close to the fires, unmindful of the heat, a barbaric figure assumed grotesque and horrible postures, while its voice rose in echoing shrillness.

Below were crowding red ones who prostrated themselves on the rocky floor.

"Fire worshipers!" The explanatory thought flashed through Dean Rawson's mind. "Here was one of their holy places, a place of sacrifice, perhaps, and he was being taken there, helpless, a captive!"