Danny O'Rourke was to carry that picture clearly in his mind--the figure that moved unhurriedly on, towering above the others, men and women, who scurried fearfully from his path. But he was to retain yet more vividly the recollection of a group of red-clad bodies that were severed at their waists as a slim tube swung--then a bursting cloud of oily smoke, and a pool of molten rock where they had been. * * * * * Something of this, perhaps, was clouding the eyes of Danny O'Rourke, Pilot of the A.F.F. a month and more later, as he sat at lookout duty in a gleaming white tower on a high peak of the Sierras. Not that the job of lookout was part of O'Rourke's duty, now that he was back in the U. S. A., but a cylinder of scarlet rested on a great rack at the base of the tower, and Danny had no wish to hear the roar of that cylinder's stern exhaust for a time. Even the novelty of flying the newest rocket-ship in the service had worn off. Besides, he had patrolled his route, and he told himself that the "Infant" needed a rest. The "Infant," better known on the records of the A. F. F. as Morgan, David E., Lookout, Station 39-G, was sleeping soundly on the elevating table where a map of the district was mounted under glass. His cherubic face was pink and white, more suggestive of the age of three than of twenty-three. And O'Rourke, glancing at him protectingly, hung up a paper to keep the sunlight from striking the young man's face. The Infant had been Danny's special charge from the day he entered the service, and now, except for the Chief and some other officials, only Danny knew that the Infant was there to teach and not to learn. For behind those eyes that might have been taken from one of Rafael's cherubim lay a brain that Danny had learned to respect. "Fifteen minutes more. I'm givin' you," he said inaudibly; "then I'll be on my way, and you'll do your own squintin' and peekin'." But the Infant's fifteen minutes were cut to that many seconds-- Danny had been looking toward the south before he had turned to gaze at the Infant: his eyes came back to the same point to take up their reconnaissance. But now, where clear sky had made a blue back-drop for rugged peaks, was a line of black. And the line, while Danny watched in disbelief, moved like a smoky serpent: its head stretched out and out while from behind it there came the ominous line of black. * * * * * All this happened in a matter of seconds, and the moving head ceased at last to move; the line no longer grew. But, where it had been at first a thin mark of black, it changed now to billowing gray. It was fifty miles away at least; but it showed clear and sharp. And the first gray had hardly bloomed from its black beginning before the long arm of Danny O'Rourke had swept the sleeping Infant to the floor, while, with the other hand, he swung an instrument of telescopic sights upon distant smoke.