"You see," Drost went on to explain, as he indicated a large mortar of marble. "I have been treating phenol with nitric acid and have obtained the nitrate called trinitrophenol. I shall fill this case with it, and then we shall have an unsuspicious-looking weapon which will eventually prove most useful to us--for it can be carried in perfect safety, only it must not be laid down." Ortmann laughed. He saw that his friend's inventive mind had produced an ingenious, if devilish, contrivance. He had placed death in that innocent-looking walking-stick--certain death to any person unconscious of the peril. Indeed, as Ortmann watched, his friend carefully filled the cavity in the brass cylinder with the explosive substance, and placed within a very strong detonator which he connected with the clockwork, winding it to the full. He then rescrewed the cap upon the fatal cylinder, replacing it in the walking-stick and readjusting the knob, which closed so perfectly that only close inspection would reveal anything abnormal in the stick. "The other stuff is there already, I suppose?" "I took it down there the night before last in four petrol-tins." "The new stuff?" "Yes. It is a picric acid derivative, and its relative force is twice as great as that of gun-cotton," was the reply of the grey-haired man. He spoke with knowledge and authority, for had he not been one of the keenest explosive experts in the German arsenal at Spandau before he had assumed the role of the Dutch pastor in England? "It will create some surprise there," remarked Ortmann, with an evil grin upon his sardonic countenance. "Your girl knows nothing, I hope?" "Absolutely nothing. I have arranged to carry out our plans as soon as possible, to-morrow night, or the night after. Bohlen and Tragheim are both assisting." "Excellent! I congratulate you, my dear Drost, upon your clever contrivance. Truly, you are a good son of the Fatherland, and I will see that you receive your due and proper reward when our brave brothers have landed upon English soil." "You are the eyes and brains of Germany in England," declared Drost to his friend. "I am only the servant. You are the organiser. Yours is the Mysterious Hand which controls, and controls so well, the thousands of our fellow-Teutons, all of whom are ready for their allotted task when the Day of Invasion comes." "I fear you flatter me," laughed Mr Horton, whom none suspected to be anything else than a patriotic Englishman. "I do not flatter you. I only admire your courage and ingenuity," was the quiet reply. And then the two alien enemies, standing in that long, low-ceilinged laboratory, containing as it did sufficient high-explosives to blow up the whole of Hammersmith and Barnes, bent over the long deal table upon which stood a long glass retort containing some bright yellow crystals that were cooling.