Derek had just fired his last round, and was preparing to climb and fly back for more ammunition, when, like a blow from a titanic hammer, a fragment of shell shattered the swiftly-revolving blades of the propeller. Other pieces of flying metal severed the aileron-controls, cut jagged rents in the doped canvas fabric, and damaged the tail planes. Switching off the now useless motor, which had begun to race furiously, Derek vainly endeavoured to glide back to the other side of the canal. The effort was beyond the power of the crippled 'bus. It was evident that, if not exactly out of control, there was very little tractability in its nature. "She's bound to crash," thought Derek. "Hope to goodness I can get clear of Fritz's line." In spite of imminent peril, and the possibility of a tremendous crash, the young pilot's nerve did not desert him. Bullets were flying past in showers of metal, for nothing pleases the Hun better than to riddle a tricolour-circled machine that is falling helplessly to earth. The actual fall was of short duration, although to Derek it seemed of interminable length. He mentally marked the spot where the ill-fated machine would crash--a shell-pitted piece of ground about one hundred and twenty yards from the first-line German trench. "Now for it!" muttered Derek, as the ground appeared to rise to greet the disabled mechanical bird. "What an unholy mess of things there'll be!" Relaxing his hold of the now useless joy-stick, and unfastening his quick-release belt, Derek raised both hands above his head, grasped and bore down the muzzle of his after machine-gun. Then, sliding under the decking of the fuselage, he waited. With a thud that shook every bone and muscle of his body, and well-nigh wrenched his arms from their sockets, the biplane struck the ground obliquely and nose first. The under-carriage splintered into matchwood, while both tyres burst with reports like that of a six-pounder gun. Then, rearing until the damaged tail stood completely on end, the distorted fuselage poised in the air like a grotesque obelisk, while the pilot, shaken and bruised, but otherwise unhurt, scrambled as quickly as he could from the wreckage and literally rolled into a shell-hole. For some considerable time Derek lay motionless, listening to the rattle of musketry and machine-gun fire, and the crackling of his burning 'bus, until the increasing heat compelled him to make for another crater. Somewhat to his surprise, he found that he could move; he could even have walked, but for the fact that it was highly desirable to keep close to Mother Earth. So close together were the craters that at one place their lips interlocked and formed a shallow gap. Through this passage Derek began to make his way, noiselessly and stealthily.