Once or twice they look back at the flaming destruction which they have wrought, all in the space of a few minutes. As they do so, a mighty column of flame and black smoke rises up into the air, and a terrific explosion takes place, which shakes the earth for fifty miles around. Yes, the T.N.T. works have gone up, and the two explosions which soon follow show that something else has gone into the sky as well. "Bravo! Krupps' has been bombed!" Dastral gives the signal for his men to turn to the westward, and to make with all possible speed for the shelter of their own lines. But enemy 'planes are in rapid pursuit, and there are two lame ducks in the flight. It means another two hours' journey, and there is no chance for the lame ducks if they are further molested. The leader quickly decides. He has still some fight left in him, and so has Mac. They will escort the rest. He signals to Mac, "Take the left flank!" and Mac understands, while he himself takes the right flank. Then he orders the others to go S.S.W., for they must not infringe the neutrality of Holland by going due west. And so they proceed, until Jock signals that two of the Huns are gaining upon them. They are fast 'planes, and will do some damage if they are not dealt with. At present they are still half a mile behind and a thousand feet below them. So Dastral circles round once or twice as if to fight with them, but only one of them accepts the challenge, and opens fire at the Flight-Commander. "Rap-rap-rap-rap-rap!" comes the sound of the fire, just audible above the roar of the engines and the whir-r-r-r of the propellers. But Dastral has the weather-gage of him, for he has a thousand feet greater altitude. He waits a moment, circling round. Then, as the Boche comes up, he dives at him, as though he meant to ram him, for he knew this would unnerve the enemy more than anything else. At the same moment he treats the Boche to three sudden bursts of fire from his Lewis gun. It is quite enough for the enemy. He has outdistanced his friends, and does not care to engage this air-devil of an Englishman alone, so he swerves round, and hauls off a little, hoping that the Britisher will be sufficient of a fool to pursue him, but Dastral returns to his command, so that he may shepherd the lame ducks through any further peril that may come upon them. Again and again on that long journey back he has to turn and fight, and often Mac accompanies him. At length, half frozen to death, with their eyes smarting so that they can scarcely see, one of them sights the relief squadron which has come to meet them and escort them back to safety. Half a squadron has come to meet them, good fighters, all fresh and ready for any hostile aircraft that cares to take the challenge. And so, after nearly six hours of a trying ordeal, "B" Flight returns safely to the shelter of the aerodrome behind the British lines. CHAPTER IX THE GIANT WAR-PLANE