Increasingly mystified, he caught up his rifle and strode on down the passage, at that moment illuminated by the last unearthly rays of the aurora borealis. A single, dazzling beam played before him like a powerful searchlight, to light a high vaulted tunnel of basalt rocks which were distorted by some long-gone convulsion of the earth into a hundred weird cleavages and faults. For that brief instant he found he could see perhaps a hundred feet down into a high roofed passage, along the top of which poured a tremendous stream of billowing, writhing steam. "If this doesn't beat all," he murmured; but for all of his apprehension he did not pause. Those bloody splashes bespeaking Alden's pressing need urged him on. "Looks like I'm taking a one way trip into Hell itself. Well, we'll soon see." Slipping and sliding over an almost impassable array of black rocks and boulders, Nelson fought his way forward, conscious that with every stride the air grew damper and warmer. Soon trickles of sweat were pouring down over his chest, tickling unbearably. Then all at once the ray of light faded, leaving him immersed in a blackness equalled only by the gloom of a subterranean vault. He stopped and, resting his rifle against a nearby invisible rock, threw back the parka hood and pulled off his gloves. He was amazed to feel how warm the strong air current was on his hands. "Beats all," he muttered heavily. "I wonder where they've taken Alden?" * * * * * Meanwhile his hands groped through fur garments now wet with melted-snow and ice particles, searching for the catch to open that pocket in which lay a small but powerful electric flashlight, an instrument without which no far-flying aviator finds himself. After a moment's fumbling, his yet stiffened fingers encountered the cylindrical flash and, with a low cry of satisfaction, he drew it forth to press the button. "Mighty useful. I--" The words stopped, frozen on his lips. Before the parka edge his close cropped hair seemed to rise, and his breath stopped midway in his lungs. Sharp electric shocks shook him, for there, half revealed in the feeble flashlight's glare, was a sight which shook his sanity to the snapping point. Not fifty feet away two eyes, large as dinner plates, with narrow vertical red irises, were trained on him. Rooted to the ground by the paralysis of utter horror, Nelson saw that their color was a weird, unhealthy, greenish white, rather like the color of a radio-light watch dial. Strangely intense, these huge orbs wavered not at all, filling him with an unnameable dread, while the strong odor of musk assailed his nostrils. The flashlight slipped from between Nelson's fingers and, no longer having his thumb on the button, flickered out.