For the second time within twelve hours Derek Daventry made a journey by car to Le Tenetoir aerodrome. On the second occasion it was to give evidence against the airman-spy Count Hertz von Peilfell; but upon arriving at his destination he found that the court-martial had been summoned to no purpose. The prisoner had escaped, and, although his description had been circulated all along the Allied front and over the back-areas, the Count was still at large.

Amongst the British airmen the general tone of expression was one of sympathy—as far as sympathy could be extended to a Hun. Von Peilfell was a crack airman; his r?le of spy was quite in accordance with modern warfare, for both British and French air-craft had frequently landed spies well behind the German lines. It was almost unanimously felt that, if Count von Peilfell were to fall, a fitting end to him would be in aerial combat. If he fell on territory occupied by the Allies he would be buried with full military honours; if on soil temporarily held by the Huns, then a British aeroplane would doubtless circle over the funeral-party and drop a wreath bearing a tribute to the crack Hun flyer\'s prowess.

But sterner work was on hand. It was a carefully-kept secret that at dawn on the next day following the spy\'s escape a frontal attack was to be delivered upon the Huns, still holding a strongly-fortified section of the line—a front of twenty miles, protected on both flanks by broad canals, and defended by mazes of trenches and barbed-wire entanglements.

Once this section were pierced, the whole German line would be in danger. Army corps would be practically surrounded and forced to surrender, while a broad wedge would be driven between the Huns in Flanders and those who were stoutly resisting the Franco-American troops in the neighbourhood of Metz.

An infantry attack would be too costly. Heavy artillery bombardment would give the Boches an inkling of what was about to develop. On this account the British guns had of late remained comparatively inactive, in order to lull Fritz into a state of false security.

So the assault was to be delivered by tanks, supported by relatively small detachments of infantry, while the R.A. F. were ordered to co-operate to their utmost capacity. Every available machine fit for offensive work was to be employed in the operations, the idea being not only to paralyse the Huns in the firing-line, but to prevent reinforcements and supplies reaching them. In brief, the whole of a certain German sector was to be wiped out.

At five in the morning, or two hours before dawn, the tanks were to start upon their grim errand. Every square foot of ground occupied by the enemy in the coveted sector had been photographed and re-photographed by daring airmen. The work had been efficiently performed, but at a cost, as the long R.A.F. casualty list testified. It was not in the heat of combat that these daring aerial photographers had been shot down, but in the cold, methodical pursuit of an art that the demands of modern warfare had relentlessly absorbed.

With an accurate knowledge of the nature of the terrain the task of the tanks had been rendered fairly straightforward. There were, of course, hidden pitfalls which the almost all-seeing lens of the camera failed to detect: cleverly-camouflaged gun-emplacements and nests of machine-guns that were not shown on the finished photograph-prints; but even here the work of the airman was evident. Cryptic markings on the prints gave the staff officers certain clues—an anti-aircraft battery here; a booby-trap there, an observation-post in that place. The science of detecting screened pitfalls was almost as perfect as the skilful art of camouflage.

There were tanks and tanks. The ground trembled under the pulsations of their powerful engines. Whippets, male tanks, female tanks, "Rolls" tanks capable of doing twenty miles an hour with their 250-h.p. engines; tanks mounting six hundred quick-firers, tanks bristling with machine-guns—a veritable armada of land-ships moving forward in what appeared to be a solid, compact mass.

They moved slowly at first, each section led by an officer on foot towards the as yet invisible German lines. There had been a spell of quietude on this part of the front of late. The Huns considered their defensive works so perfect that a frontal attack would be impossible, and, being let severely alone, they had refrained from their usual lavish display of star-shells.

Grunting, groaning, coughing; ejecting vile, sulphurous fumes from their noisy exhausts, the steel-clad mastodons ambled onwards until Fritz, suddenly aware that danger was at hand, opened a furious fire that threw a dancing, lurid glare upon the crater-pitted plain over which the hordes of tanks surged like a sullen ground-swell beating upon a flat shore. Vivid red and white rockets—Fritz\'s S.O.S. signals—soared skywards, an appeal by the field-grey infantry for support from their heavy artillery.

It was at this juncture that Derek Daventry, one of the host of aerial fighters, found himself flying at a few hundred feet above the Boche lines.

In the reflected glare of the rifle- and machine-gun fire he could discern the array of tanks advancing. The slow-moving tanks were in the van, their raison d\'être to flatten down the hostile wire and pave a way for the whippets and "twenty-milers" of the land-fleet. Machine-gun bullets were rattling against their armoured snouts, while here and there bursts of vivid-red flame gave token that the anti-tank bullets—steel-cored and copper-encased missiles—had put more than one tank out of action.

All this Derek took in as the result of a few seconds\' flight. Then, over the hostile front, his work began. In darkness, save for the intermittent flashes of the guns, the British \'planes sped to and fro. Unavoidable collisions brought friends crashing to earth; oft-times the machines were flying blindly through clouds of black, nauseating smoke. Rocking, side-slipping, bumping, and banking, the aerial-fleet continued its work in hammering with the land-armada of tanks. Machine-gunning, bombing, and dropping poison-gas cylinders, the airmen hovered remorselessly over the now-demoralized Boches, while the tanks, surging onwards, beat down acres of barbed-wire and flattened out whole sectors of trenches.

Derek had just fired his ninth tray of ammunition when he felt the joy-stick give. A fragment of shell had severed the "nerve-centre" of the biplane, and the \'bus was now practically out of control. A touch upon the rudder-bar turned EG 19 in the direction of "home", but almost immediately the engine "konked". In the darkness it was impossible to see what had happened, but another fragment of shell had lodged fairly in the magneto.

EG 19 had to come down. How she came down depended upon sheer luck, since the skill and nerve of the pilot were useless to avoid the threatened calamity.

Derek steeled himself to meet the tremendous crash, but the shock never came. By one of those eccentricities of movement that aerial-craft occasionally perform, the biplane flattened out within twenty feet of the ground, dipped her nose, and then pancaked upon the shelving side of a large shell-crater. Without a scratch the pilot scrambled out of the fuselage and gained the ground.

He promptly threw himself at full length in the stiff mud that lay in the bottom of the crater, and listened to the appalling racket overhead. Shells of light calibre were screeching and bursting all around, their uproar punctuated by the heavier concussion of aerial-bombs. A crescendo of machine-gun fire added to the deafening roar, while the hail of bullets directed upon the imperturbable tanks sounded like a continuous tattoo.

Almost on the lip of the crater a large tank had come to a standstill. Two jagged holes in her fantastically-painted sides showed that a Hun anti-tank gun had scored direct hits, but whether these had put the mobile fort out of action Derek was unable to determine.

While debating whether it would be safer to tak............