"That's just it! This is the nerve center of the entire Magogean defense system. Look ... look below, there!" Gary gestured to the window slit by which they were huddled. Through it could be seen the lower court of the Palace Royal and several streets of Khundru beyond. All had been emptied of vehicular traffic and were aswarm with fighting men prepared to repel any invasion attempt. "They've got the Palace guarded to the hilt ... but the main control tower doesn't have a man around it!" Lark chuckled cheerfully. "Just like the Magogeans. Dr. Kang's been saying all along they don't have good sense. So much the better for us. Come on ... let's get going. We've got to open that barrier. "Well, all right," agreed Gary. "But be careful. I don't like this." * * * * * So they crossed the last open space between their present post and the partially isolated control tower, a domed minaret of a building constructed within the palace walls but remote from other portions of the edifice. Serving to strengthen Gary's suspicions, the door of this tower was not even locked, but yielded readily to their pressure. Within this dome the thrumming drone of motors sounded more insistent than ever. It throbbed in their ears, their brains, their veins, like the slow and deadly dripping of a creeping poison. It was an audible magnet which drew them to the innermost chamber. And here again--stunningly!--was the door unlocked! Its latch clicked at Gary's pressure. The heavy door swung slowly open, and a bright room yawned before them; a tremendous, vaulted chamber in which were mounted gigantic instruments of almost unguessable size and power. The control panels governing these instruments were set on high walls, but as they entered Gary saw that a single figure, garbed in smock and apron of laboratory white, head encased in a heavy visionplated shield similar to that used by welders, sufficed to keep all this intricate paraphernalia in working order. This single technician was darting back and forth before his control banks, here touching a vernier, there readjusting a rheostat, elsewhere depressing a stud which performed some unfathomable duty. At sight of this single lab man, O'Day's exultation could no longer be restrained. With a gleeful cry he charged into the room, handgun drawn and menacing. His voice cried in swift command. "All right, you at the controls there! Turn around, and put your hands up--_Up_, I said!" And then--too many things happened at once! There came a sudden gasp from Penny's lips. "Lark! It's--" And a frightened scream from Nora Powell. Metal clanged noisily as the great door clanged behind the four invaders. A bolt thick as a man's arm jarred into place. And even as the four whirled to comprehend this phenomenon, an all too horribly familiar voice repeated O'Day's order.