He climbed for the skies, then, as rectangles of light showed below and planes were thrust out of their lighted hangars. Four huge conflagrations were begun. One was close by a monster rounded tank, and Bell watched with glistening eyes as it crept closer. Suddenly--it seemed suddenly, but it must have been minutes later--flame rushed up the sides of that tank, there was a sudden hollow booming, and fire was flung broadcast in a blazing, pouring flood. "Their fuel tank!" said Bell, his eyes gleaming in the ruddy light from below. He shut off his landing lights and went upward, steeply. "I've played hell with them now!" A thousand feet up. Two thousand. Two thousand five hundred.... And suddenly Bell felt cold all over. The instrument board! The motor was hot. Hot! Burning! He shut it off before it could burst into flames, but he heard the squealing of tortured, unlubricated metal grinding to a stop. He leveled out. It was strangely, terribly silent in the high darkness, despite the roaring of wind about the gliding plane. The absence of the motor roar was the thing that made it horrible. "Paula," said Bell harshly, "one of those plugs came out, I guess. The motor's ruined. Dead. The ship's going to crash. Ready with your parachute?" * * * * * It was dark, up there, save for the glare of fires upon the under surface of the wings. But he saw her hand, encarmined by that glare, upon the combing of the cockpit. A moment later her face. She turned, light-dazzled, to smile back at him. "All right, Charles." Her voice quavered a little, but it was very brave. "I'm ready. You're coming, too?" "I'm coming," said Bell grimly. Below them was the city of The Master, set blazing by their doing. If their chutes were seen descending.... And if they were not.... "Count ten," said Bell hoarsely, "and pull out the ring. I'll be right after you." He saw the slim little black-clad figure drop, plummetlike, and prayed in an agony of fear. Then a sudden blooming thing hid it from sight. Thick clouds of smoke lay over the lights and fires below. Bell stepped over the side and went hurtling down toward the earth in his turn. (_To be continued_) [Advertisement: ] The Cavern World _By James P. Olsen_ [Illustration: _He aimed it, and the Thing gripping him was hurled back upon the others._] [Sidenote: A great oil field had gone dry--and Asher, trapped far under the earth among the revolting Petrolia, learns why.] "Impossible! What sort of creatures would they be, that could live two miles beneath the surface of the earth? Surely, Asher, you are joking!"