That day machines were up in hundreds. The sky seemed stiff with biplanes and monoplanes, all bearing the distinctive red, white, and blue circles. Each machine had a definite object in view--a set task to perform. On the other hand the Boche was chary of going aloft. Not a single black-cross machine crossed our lines. Even the famous Hun circuses kept well away from the scene, since Fritz recognized the Allied superiority in the air, and rarely, if ever, tried conclusions with superior numbers. Therein lies the difference. British and French airmen are sportsmen, ready to rush in whenever an opportunity offers, and scorning to decline a combat against heavy odds; German flyers are almost invariably cold-blooded, scientific men who calculate their chances deliberately before venturing to meet their aerial foes. Keeping Kaye's 'bus in full view, for both airmen were bound for practically the same destination, Derek flew all out, passing over the German lines at less than two thousand feet. Not an Archibald greeted his appearance. Fritz was getting tired of being strafed, and was beginning to find that it paid better to lie doggo than to invite a few bombs or a hail of machine-gun fire from passing aeroplanes. Steering partly by compass, and correcting his course by observation of prominent landmarks, Derek held on. Other 'buses passed and repassed--bombers, chasers, and reconnaissance machines--some of the pilots waving a greeting to the squat, businesslike EG 19. It was a bright, sunny day, although here and there dark clouds drifted slowly across the sun. The ground beneath was honeycombed with shell-craters, and dotted with mounds that at one time, not so very long ago, were prosperous villages. A canal, almost dry owing to the destruction of the locks, cut the landscape in an unswerving straight line, while a network of railways, most of them constructed immediately after the big German offensive, spread like a gigantic cobweb as far as the eye could see. There was plenty of smoke, for it was now the Huns' turn to set fire to their own ammunition-dumps, while at frequent intervals long-distance naval guns would drop their gigantic projectiles, that burst in a mighty cloud of black and orange-tinted smoke. Viewed from the air, the scene of the mighty battle was tame. Distance hid the hideous and ghastly details, while in the pure atmosphere the indescribable but distinctive stenches from the field of carnage were not perceptible. If distance did not exactly lend enchantment to the view it certainly threw a kindly veil over most of its shortcomings. Half an hour passed. Kaye's 'bus was still in sight. If anything, Derek was gaining on her, but in the air five minutes' start is a long one. The two biplanes were now practically alone, although a flight was visible at a great distance to the south-east.