Whistles blew shrilly amid the roar of battle. Several of the Tank-Commanders, hearing and understanding the import of the order, brought their ponderous craft to a standstill. Others began to wheel in order to give a wide berth to the highly-dangerous locality. Fifty yards ahead, and separated from them only by three almost flattened trenches, was an objective which, if gained, would be the master-key to this phase of the important operations, and yet with success in sight the nerve-racking attempt bid fair to end in failure. At this critical juncture Derek, to the surprise of the crew of the abandoned tank, suddenly sprang upon the parados. In a couple of strides he overtook the Major, and, throwing his arms round the latter's neck and planting one knee in the small of his back, bore him backwards to the earth. Then, not content with this comparatively mild form of attack, Derek pinioned the officer's wrists by means of the lanyard of his whistle. He was dragging his captive into the trench when a Tank-Commander intervened. "What on earth are you doing?" he demanded. "It's all right," replied Derek reassuringly. "The fellow's a Boche. I know him. Get the tanks to carry on." Fortunately the officer grasped the situation and had the retirement order annulled. The mammoth machines resumed their forward progress, blazing away with their quick-firers and machine-guns, until Derek found himself well in the rear in the company of a handful of men and Count Hertz von Peilfell. It was a freak of fortune on the battle-field that had played into Lieutenant Daventry's hand. The Count, having succeeded in escaping from the Le Tenetoir aerodrome, had passed through many adventures before he regained the German lines. Then, in a desperate bid to regain prestige, he had volunteered again to act as a spy. Knowing that there were many changes in the personnel of the Tank Corps, he determined to assume the rôle and uniform of a major, and await an opportunity to thwart the victorious advance of the ponderous Behemoths. Succeeding the tanks came swarms of infantry, of whom, but for the assistance of the mobile armoured forts, the Boche machine-gunners would have taken heavy toll. As it was they were able to consolidate the position already taken with but slight losses in proportion to the numbers engaged. There were engineers, busily engaged in laying telephone wires, while numerous stretcher-bearers and ambulance-men were strenuously working to remove the wounded from the stubbornly-contested field. Meantime Fritz was shelling the lost ground to the best of his ability, the guns taking impartial toll of khaki and field-grey. Having no further use for cannon-fodder that had fallen into the hands of the victorious Allies, the Boche artillerymen seemed to show not the slightest compunction at slaughtering their comrades.