"We might as well," the other agreed wearily. His was the tone of a man who has only a certain time to live. But Phil was more eager. "While there's life, there's hope," he said cheerfully. "Come on, Sue, Professor!" And he led the way forward toward the dim, distorted rock shapes in the distance. * * * * * The roof and sides of the cavern angled down into a rough, tunnel-like opening, from which the draft swept. It was a heavy air, weighted with the smell of moist earth and lifeless water and a nameless, flat, stale gas. They slowly made their way through the impeding stalagmites, surrounded by a dark blur of shadows, the ghostly phosphorescent light illuminating well only the few rods around them. Utter silence brooded over the tunnel. Phil paused when they had gone about seventy-five feet. "I left that rope behind," he said, "and we may need it. I'll return and get it, and you both wait right here." With the words he turned and went back into the shadows. He went as fast as he could, not liking to leave the other two alone. But when he had retrieved the rope and tied it to his waist, he permitted himself a last look up as he passed under the hole in the ceiling--and what he saw there tensed every muscle in his body, and made his heart beat like mad. Again there was a tiny spot of orange in the blackness above! "Professor!" he yelled excitedly. "Sue! Come here! The sphere's coming back!" There was no doubt about it. The pin-point of light was growing each second, with the flame of the descending exhausts. Guinness and his daughter ran from the tunnel, and, guided by Phil's excited ejaculations, hurried to his side. Their eyes confirmed what his had seen. The earth-borer was coming down! "But," Guinness said bewilderedly, "those rockets were enough to lift him!" This was a mystery. Even though ten rockets were on--ten tiny spots of orange flame--the sphere came down swiftly. The same force which some time before had lifted it slowly up was now insufficient. The roar of the tubes rose rapidly. "Get back!" Phil ordered, remembering the danger, and they all retreated to the mouth of the tunnel, ready to peep cautiously around the edge. Holmes' jaws were locked tight with grim resolution. Quade was coming back! he told himself exultantly. This time he must not go up alone! This time--! But his half-formed resolutions were idle. He could not know what frightful thing was bringing Quade down--what frightful experience was in store for them all.... CHAPTER IV _Spawn of the Cavern_