The next instant a cloud of pungent, burning powder struck Entwistle full in the face. The sudden, agonising pain as the grains filled his eyes took the Secret Service agent completely off his guard. Gasping for breath, and holding both hands to his face, he staggered blindly against the wall. Even in his physical torment he could hear von Preussen running swiftly. In the moment of his triumph a craven trick had robbed Entwistle of his prey. CHAPTER XXV TRAPPED COLD, grey dawn was stealing over the North Sea. Hull down to the east'ard, her cage-mast just showing above the horizon, lay the Hoorn Reefs Lightship. Off the tail of the bank that fringes Denmark's shores Hun submarines were in the habit of bringing up and receiving wireless orders before venturing through the inner mine-fields either to the mouth of the Elbe or northwards to the Baltic through the Kattegat. Q 171 was moving slowly through the greyish-green water. Her triple torpedo-tubes were ready with their deadly complements; her quick-firers, trained fore and aft after the manner of U-boats returning to their bases, were ready for action at a moment's notice. The torpedo-men and gun crews, sheltering under the lee of the dummy conning-tower, were keenly on the alert, watching their commanding officer as he, in his turn, watched the broad expanse of sea over which the rising sun would shortly throw its slanting rays. Supporting himself by the shaft of the periscope, which, like the conning-tower, was a "dud," Morpeth again and again raised his prism-binoculars to his eyes. Just below him stood Wakefield, conscious of a peculiar sensation of mingled doubts and hopes. He, too, shared with Morpeth the feeling that the climax was at hand. The great stunt that was to deal a terrific blow to Germany's campaign of unrestricted warfare was imminent. Would it succeed? The plan of operations was daring in its simplicity. According to information obtained from a British Secret Service agent in Kiel, two giant submarine-cruisers were leaving the German Baltic port, passing through the Imperial Kiel Canal during the hours of darkness, and leaving Brunsbuttel the following night for the Hoorn Reefs rendezvous. Here they were to take on board two experienced U-boat commanders from submarines expected to be homeward-bound from the Irish Sea, and then proceed to the Atlantic seaboard of the United States. Capable of keeping the sea for a period of sixty days without having to re-fuel or re-provision, these submarine-cruisers were a direct menace to the Allies in general and to Uncle Sam in particular. Consequently, if Morpeth's plans were successful and he were able to destroy both submarine-cruisers before the returning U-boats arrived at the rendezvous, the moral effects of the mysterious disappearance of two brand-new additions to Germany's under-sea fleet would be more far-reaching than their actual loss.