Instantly, efficiently, without a word in reply to the eager command of Prester Kleig, General Munson relieved Professor Maniel at the apparatus which Maniel called the Vibration-Retarder, his invention which he had combined with audible teleview to complete this visual miracle of the Secret Room. Professor Maniel stepped to where Prester Kleig was sitting. Prester Kleig put fingers to his lips for silence, and an expression of surprise crossed the wrinkled dead-white face of the Professor. Before Kleig could speak, however, there came a signal from somewhere outside the Secret Room, a signal which said that the doors were being opened and that a personage was coming. The Secret Agents looked at one another in surprise, for every man who had a right to be inside the Secret Room was already present. "I know," said Kleig, his face a mask of terror. "It is Charmion and Carlos Kane! Moyen, the devil, has managed to make sure of obedience to his orders!" The Secret Agents turned back to the screen, upon which the view of the first aerial brush of the American flyers with the minions of Moyen, in their aero-subs, was drawing to a terrible close. For, as the aero-sub commanders had played with the warships, which had no human beings aboard them, so now did they play with the planes of the Americas. * * * * * One American flyer, startled into a frenzy by the fate of his fellows, put his helicopter into action, and leaped madly out of the midst of the battle. Instantly an aero-sub zoomed, skyward after him. Again that golden streak of light from the nose of an aero-sub, and the helicopter vanes and the slender staff upon whose tip they whirled vanished, shorn short off above the vane-grooves in the top of the wing! The plane dropped away, fluttering like a falling leaf for a moment, before the aviator started his three propellers again. A cheer broke from the lips of Prester Kleig as he watched. The commander of that particular aero-sub, apparently contemptuous of this flyer who had tried to cut out of the fight, allowed him to fall away unmolested--and the American, driven berserk by the casual, contemptuous treatment accorded him by this strange enemy, zoomed the second his propellers whirred into top-speed action, and raced up the sky toward the belly of the aero-sub. "If only the aero-sub has a blind spot!" cried Prester Kleig. * * * * * In that instant a roaring crash sounded in the Secret Room as the American plane, going full speed, crashed, propellers foremost, into the belly of the aero-sub. And the aero-sub, whose brothers had seemed until this moment invincible, did not escape the wrath of the American--though the American went into oblivion with it! For, welded together, American plane and aero-sub started the eight thousand feet plunge downward to the sea! "Watch!" shrieked Munson. "Watch!"