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. * * * * * In 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. * * * * *