The air was filled with swelling clouds. He saw them before the blast struck where he stood. The great building shuddered at the impact. There were things falling from the clouds, wrecks of planes, blazing and shattered. Still came others; he saw them faintly through the clouds. They came in from the West; they had gone far to gain altitude. They drove down from the heights--the enemy had drifted--they were over the bay. More clouds, and another blast thundering at the city. There were specks, Thurston saw, falling into the water. Again the invaders came down from the heights where they had escaped their own shattering attack. There was the faint roar of motors behind, from the south. The squadron from Washington passed overhead. They surely had seen the fate that awaited. And they drove on to the attack, to strike at an enemy that shot instantly into the sky leaving crashing destruction about the torn dead. "Now!" said Cyrus Thurston aloud. * * * * * The big bulbs were back. They floated easily in the air, a plume of vapor billowing beneath. They were ranging to the four corners of a great square. One plane only was left, coming in from the south, a lone straggler, late for the fray. One plane! Thurston's shoulders sagged heavily. All they had left! It went swiftly overhead.... It was fast--fast. Thurston suddenly knew. It was Riley in that plane. "Go back, you fool!"--he was screaming at the top of his voice--"Back--back--you poor, damned, decent Irishman!" Tears were streaming down his face. "His buddies," Riley had said. And this was Riley, driving swiftly in, alone, to avenge them.... He saw dimly as the swift plane sped over the first bulb, on and over the second. The soft roar of gas from the machines drowned the sound of his engine. The plane passed them in silence to bank sharply toward the third corner of the forming square. He was looking them over, Thurston thought. And the damn beasts disregarded so contemptible an opponent. He could still leave. "For God's sake, Riley, beat it--escape!" Thurston's mind was solely on the fate of the lone voyager--until the impossible was borne in upon him. The square was disrupted. Three great bulbs were now drifting. The wind was carrying them out toward the bay. They were coming down in a long, smooth descent. The plane shot like a winged rocket at the fourth great, shining ball. To the watcher, aghast with sudden hope, it seemed barely to crawl. "The ray! The ray...." Thurston saw as if straining eyes had pierced through the distance to see the invisible. He saw from below the swift plane, the streaming, intangible ray. That was why Riley had flown closely past and above them--the ray poured from below. His throat was choking him, strangling.... * * * * *