Cumberleigh, Blenkinson and Jefferson found themselves escorted below in double quick time. When fear hangs on the heels of a U-boat's crew the promptness to execute an order borders on panic. Literally hustled along a narrow alley-way bristling with dozens, nay, scores, of valve-wheels, they were bundled into a dark, moisture-laden recess that at one time contained a quantity of consumable stores. The door was slammed and locked, and the three R.A.F. officers found themselves prisoners of war under highly objectionable circumstances--trapped in a U-boat. Giving another glance skywards and all around the horizon, von Preugfeld walked aft to the hatchway through which von Preussen had disappeared. "I'll see you in the ward-room in less than five minutes, von Preussen," he said. "Apparently this affair requires an explanation. But what has become of the fourth Englishman?" "Still on board," replied the spy. "He's trying to evade capture." "There is an alternative," remarked the ober-leutnant grimly. "He's welcome to it." Making his way back to the outside of the conning-tower, von Preugfeld noted that his order concerning the sailing-boat had been carried out. Levelling his binocular, he scanned the shelving deck of the X-lighter. There was no sign of life on board X 5. Ringing for half speed, von Preugfeld increased the distance between the U-boat and her prize to three hundred yards. "Give her a round amidships!" he ordered. The U-boat rolled sluggishly to starboard under the recoil of the gun. Almost simultaneously with the report of the weapon came the crash of exploding shell. Amidst a welter of foam and yellow smoke X 5 disappeared beneath the waves, leaving the water dotted with floating debris in the shape of buoyant articles released from her hold by the shattering of her hatches. For a full half-minute the ober-leutnant kept the flotsam under observation; then, satisfied that his work of destruction had been accomplished in its entirety, and that to remain on the surface much longer after the roar of the explosion was hazardous, he turned to von Loringhoven. "Down to twenty-five metres," he ordered. "Course due west at eight knots for ten minutes. Then let her sound." Leaving the unter-leutnant to carry out his instructions, von Preugfeld made his way to the cabin where the returned spy awaited him. "I hardly expected to see you so soon, Karl," he began. "I hope I haven't disturbed your elaborate plans." "You have," replied the spy, with marked emphasis. "_Himmel!_ How is that? Were you taken into the confidence of these English officers, and were your investigations a secret project that was being experimented upon to the disadvantage of the Fatherland?" "You have put me to considerable inconvenience," replied von Preussen. "My kit is at an hotel at Auldhaig." "No compromising documents, I hope?" asked the kapitan anxiously.