"Lord above!" breathed Bohannan, chewing at his nails. "We're off!" Neither the Master nor Captain Alden moved, spoke, manifested any excitement whatever. Both might have been graven images of coolness. The Celt, however, got up and leaned at the window-jamb, unable to keep still. He turned suddenly to Alden. "Come, man!" he exclaimed, half angrily. "Got no heart in you, eh? No interest? Come along out of that, now, and see what's what!" He laid hold on the captain, and drew him to the window as the airship accelerated her plunge along the rails. The hum of the propellers had now risen to a kind of throaty roar; the craft was shaking with strange quivers that no doubt would cease if she but once could launch herself into the air. Under her, in and in, the shining metal rails came running swiftly and more swiftly still, gleaming silver-like under the vivid beam of the searchlight. Wind began to rise up against the glass of the pilot-house; the wind of _Nissr's_ own making. Cool as if in his own easy-chair in the observatory, the Master sat there, hand on wheel. Then all at once he reached for the rising-plane control, drew it over, and into the telephone spoke sharply: "Full speed ahead, now! Give her all she's got!" A shout, was it? Many shouts, cries, execrations! But where? Over the roar of the propellers, confused sounds won to the men in the pilot-house. And all at once, by the dim aura of diffused light reflected from the huge beam, the major saw dim figures running, off there to the left, among the buildings of the stockade. "For the Lord's sake!" he cried, amazed, with drooping jaw. "Men--after us! Look there--_look_!" The Master remained utterly impassive, eyes keen on the in-rushing track, now close to its abrupt ending over the vacancy of space. Captain Alden's pupils narrowed, through the mask-holes, but he said nothing. Bohannan gripped the captain's shoulder painfully, then reached for the pistol in his own holster. "They're on to us!" he vociferated. "Somebody's got wise--they're--" Little red spurts of fire began to jet, among the buildings; the crackling of shots started popping, like corn-kernels exploding. Dark figures were racing for the Palisade gate--the gate where, if any slightest thing went wrong with track or giant plane, the whole vast fabric might crash down, a tangled mass of wreckage. Then it was, that for the first time in all his knowledge of the Master, Bohannan heard the strange man laugh. Joyously he laughed, and with keen pleasure. His eyes were blazing, as he thrust the rising-plane lever sharply up. More shouts volleyed. From somewhere back there in the body of the ship, a cry of pain resounded. Bohannan flung the window-pane to one side, and blazed away like mad at the attackers. A shatter of broken glass burst into the pilot-house. Alden, catching his breath, quivered. He uttered no outcry, but his right hand went across and clutched his wounded left arm.