James Quade crumpled at the brink; "It's the end!" he moaned. "We can't go farther! It's the end of the draft!" The hole blocked their forward path completely. They could not go ahead.... In seconds, it seemed, the slithering that told of the monster's approach sounded from behind. Sue's eyes were already fixed on the awful, surging mass when a voice off to one side yelled: "Here! Quick!" It was Phil Holmes. He had been scouting through the gloom, and had found something. The other three ran to him. "There's another draft going through here," he explained rapidly, pointing to an angled crevice in the rocky wall. "There's a good chance it goes to the cavern where the sphere and the hole to the surface are. Anyway, we've got to take it. I'd better go first, after this--and you, Quade, last. I trust you less than the monster behind." He turned and edged into the crack, and the others followed as he had ordered. Quickly the passageway broadened, and they found the going much easier than it had been before. For perhaps ten minutes they scrambled along, with the draft always on their backs and the blessed, though faint, fire of hope kindling again. In all that time they did not see their pursuer once, and the hope that they had lost it brought a measure of much needed optimism to drive their tired bodies onward. They found but few time-wasting obstacles. If only the tunnel would continue right into the original cavern! If only their path would stay clear and unhindered! But it did not. The sound of Phil's footsteps ahead stopped, and when Sue and her father came up they saw why. "A river!" Phil said. * * * * * They were standing on a narrow ledge that overhung an underground river. A fetid smell of age-old, lifeless water rose from it. Dimly, at least fifty feet across, they could see the other side, shrouded in vague shadows. The inky stream beneath did not seem to move at all, but remained smooth and hard and thick-looking. They could not go around it. The ledge was only a few feet wide, and blocked at each side. "Got to cross!" Phil said tersely. Quade, sickly-faced, stared down. "There--there might be other things in that water!" he gasped. "Monsters!" "Sure," agreed Phil contemptuously. "You'd better stay here." He turned to the others. "I'll see how deep it is," he said, and without the faintest hesitation dove flatly in. Oily ripples washed back, and they saw his head poke through, sputtering. "Not deep," he said. "Chest-high. Come on." He reached for Sue, helped her down, and did the same for her father. Holding each by the hand, Sue's head barely above the water, he started across. They had not gone more than twenty feet when they heard Quade, left on the bank, give a hoarse yell of fear and dive into the water. Their dread pursuer had caught up with them.