Insane or not, old Luke Evans had concealed the tiny model of the camera-box to good purpose. As he swept the black beam around him, the whole mass of buildings sprang into luminosity, the figures of a score of men, grouped together, and advancing in a threatening mass, some distance away--and more. Two airplanes, standing side by side upon the tarmac, just in front of the hangar--not mere pursuit planes, but six-seaters, formidably armed, with central turrets and bow and rear guns, and propellers revolving. Two mechanics stood staring in the direction of the little group. "I'm with you," gasped Hargreaves. "I'm not a military man, but I've got fighting blood, and I come of a fighting race." Dick leaped and once more swung the iron bar. The nearer of the two mechanics went down like lead, the second, seeing his companion bludgeoned out of the air, turned and ran. Dick shouted, pointing. Fredegonde jumped into the plane, and the President scrambled in behind her. The group, dismayed by the black beam, which Luke Evans was now turning steadily upon them, had halted irresolutely. But suddenly a head appeared, moving swiftly through the air toward the plane. It was Von Kettler, with hood flung back, the face distorted with rage and fury. At his yells, the whole crowd started forward. Dick leaped into the central cockpit, swung the helicopter lever. Something spitted past his face, and a long streak appeared on the turret, where the gas-paint had been scored. But he was rising, rising into that increasing wind.... * * * * * He heard a yell of triumph behind him. And that yell of Von Kettler's was his undoing. There is the telepathy between close friends, but there is also telepathic sympathy between enemies, and in an instant Dick understood what that shout of triumph portended. He was rising into the line of magnetic force that would anchor his airplane helplessly, and leave it to be jerked down and held at Von Kettler's mercy. He released the helicopter lever and opened throttle wide. For an instant the heavy plane hung dangerously at its low elevation, threatening to nose over. Then Dick regained control, and was winging away toward the sea, while yells of baffled fury from behind indicated the chagrin of his enemies. He glanced up. Thank heaven the dirigible had not approached the trap. It was apparently circling overhead. Of course the observers had seen nothing, had no conception that the headquarters of the Invisible Empire lay below. And yet it seemed to be drifting aimlessly back toward the fleet--erratically, as if not under complete control. And Dick could see the ships about a mile offshore, apparently drifting too. They were moving as no American squadron ever moved since the day the first hull was launched, for some of them, turned bow inward toward others, seemed upon the point of collision, while others were lagging on the edge of the formation, as if pointing for home.