Once more the red ship fell swiftly under Danny's hand. As before, the valley yawned like the living threat of a volcano in eruption. But this time, instead of the whining nitro-producers, there came from beneath the ship a discordant shriek like nothing that the quiet mountains had ever heard. And Danny's fingers played over a strange keyboard whose three keys were rheostats, and the crashing discord below rose to a horror of sound that tore and battered at the ship's thick walls to set the nerves of the crouching man a-jangle. But his eyes, watching through a lookout below, saw strange disturbances of the flames; he saw the masses of flame shiver as if stricken--fall apart--vanish! And he held the sound controls at that same horrendous shriek while his ship swept on and the thunder of her passing was lost in the pandemonium that went before. But the valley, when the red ship had passed, was a place of charred skeleton trees--of gray, swirling ashes, and of embers, here and there, that blew back to life only to be smothered by the gases of the ships that followed in his wake. And the voice that spoke from the instrument beside him still spoke drily. "There's fifty miles more of that ahead," said the voice. "Just keep moving along; we'll mop up behind you.... Oh, and by the way, O'Rourke, give my congratulations to the Infant on the success of his invention. His sound-dampener is some little doodad; we'll be needing more of them, I should say." * * * * * It was an hour or more later at the Headquarters of the Mountain Division that the Chief amplified that remark in a way he himself could not have foreseen. He had been talking to Danny, and now on the wall of an adjoining room, where men sat at strange instruments, a red light flashed. "We still don't know what started it all," the Chief was saying. "But it made a fine tryout for Morgan's invention. If I thought you and he could do it, I would believe you had started that fire yourselves for a"--his voice rose abruptly to a shout--"Man! There's the red on the board--a general alarm!" "Throw the big switch!" he roared. "Cut us in, quick! Cut us in!" Danny O'Rourke, under any ordinary circumstances would have been hugely amused at the extraordinary sight of the Chief of the Mountain Division in a ferment of excitement that was near hysteria. But the flashing of the red that swept like a finger of flame across every station number of the big board did not mean that ordinary matters were at hand. A voice was speaking; its high-pitched shrillness showed that the excitement of the moment was not confined to the office of the Mountain Division alone.