Torringham aerodrome, to which Derek was posted, was a comparatively new station situated somewhere in Essex. It formed part of the outer aerial defences of London, and had not yet received its full establishment. Probably a marked disinclination on the part of the Boche to tempt fate amid the aerial net defences and improved anti-aircraft batteries over and around the city was responsible for the fact that there were few opportunities for the Torringham pilots to distinguish themselves. Also, the growing superiority of British and Allied airmen on the Western Front, and the reprisal raids upon the Rhine towns, kept the Hun airmen pretty much occupied, and London, in consequence, enjoyed a period of security. Nevertheless there was always the possibility of a daring Boche attempting to sneak over the metropolis under cover of darkness, and the British airmen stationed around London had to be constantly on the alert. It was on the eighth evening following Derek's arrival at Torringham that the period of comparative inaction was broken. There happened to be a dance in progress, to which the officers of the depot had been invited. "I don't think I'll take it on, old man," replied Daventry in answer to a brother officer's suggestion. "I've quite a dozen letters to write, and I want to turn in early. Hope you'll have a good time." So Derek sat in solitary state in the practically deserted ante-room while the revellers proceeded by motor to the scene of the festivities--a distance of nearly thirty miles. "That's a good job done!" exclaimed Derek drowsily when the last of his correspondence was finished. "By Jove, it's nearly midnight! I'll sleep like a top to-night, unless the returning roysterers rout me out of my bed." It seemed to the young officer as if he had not been asleep more than a couple of minutes when the electric light in his rooms was switched on and a hand grasped his shoulder. "Turn out, you blighter!" exclaimed a voice, which Derek failed to recognize as that of the Officer of the Watch. "They're coming over!" "Chuck it, old bird!" protested the still sleepy man. "If you want to rag anyone, try someone else." "No kid," continued the O.W. "We've just had a telephone message through to say that a group of Gothas passed over Harwich five minutes ago making towards London. You're the only pilot left on the station, so you'll have to go up." Derek leapt out of bed and hurriedly threw on his clothes. He was not at all charmed with the prospect, for Torringham lay considerably off the course usually followed by the Hun raiders. To be literally hauled out of bed in the small hours of the morning, and to ascend on a pitch-dark night without any degree of certainty of being within thirty miles of a Boche airman, seemed "hardly good enough".