His deep, heavy voice rolled out over the vast room with awesome effect, breaking as it did the unearthly silence. He was chanting, uttering an invocation or prayer. The words came to my ears, thick and blurred, so that I understood few of them. But the effect was one of utter solemnity--the darkness, the massed, silent crowds above, and that one deep voice speaking on, rising and falling. For minutes the voice rumbled on, then abruptly ceased. There was another full minute of the strange silence, and a tremendous ringing note sounded. Even after it had died, the echoes of it beat in my ears like ghostly carillons of tiny, elfin chimes. And as it died away, there was a heavy, grating sound and the whole vast metal floor abruptly sank down some six feet into what appeared to be a gigantic smooth-walled shaft, then slid sidewise with another grating jar, vanishing into some aperture prepared for it. And where the floor had been was now a tremendous circular abyss, a straight-sided pit of such titanic depth that, looking down into it, I fell weakly to my knees and was seized with sudden nausea. I stood on the very edge of the abyss, on the ring of black flooring that was its rim. And down from that rim, the stone sides of the great shaft fell smoothly to an unguessed depth. Far, far below, I seemed to see glimmering lights that winked faintly. And I saw, too, that the spiral staircase which circled the great room's interior from floor to roof continued on down beneath the floor and circled around and around this circular chasm in the same way, winding down into the unguessed depths below. I felt Denham pulling me back from the edge of the shaft, beside which I lay. Dimly I realized that all in the great building were now chanting, rolling forth the same invocation as the black-robed leader. Far above, now, at the very ceiling or roof of the cylinder, a light burgeoned out, a burning purple beam that clove its light down through the dim haze and shadows around it. A moment it hung there, then there was a faint sigh of wind, a puff of icy air, and down, straight down from the vast hall's roof, there raced like a misty plummet--the Raider! It flashed down until it hung on a level with myself, in midair, poised at the very center of the circular abyss and floating there effortlessly. It hung there, its gray mass changing, fluxing, interlacing, while at its center hung the three little orbs of purple light, steady and unwinking. From all the massed thousands on the balconies a sigh of worship went up. The chant rolled out, louder, fiercer, and through it sounded another single ringing note. There was another whistle of wind, and the three purple orbs of the Raider flashed to green, while the solid but fluxing mass of it changed to a spinning cloud of gray vapor, that swirled rapidly around the central lights. Another fierce gust of wind smote me, and abruptly the Raider had vanished.