The pair ascended the stairs to the carefully locked room in the roof, that long, well-equipped laboratory wherein Theodore Drost spent so many hours daily experimenting in the latest discovered high-explosives. After Drost had switched on the light he carefully closed the door, and then, crossing to a long deal cupboard where hung several cotton overalls to protect his clothes against the splash of acids, he took out his military gas-masks--those hideous devices with rubber mouth-pieces and mica eye-holes, as used by our men at the front. "It is always best to take precautions," Drost said, as he handed his companion and taskmaster a helmet. "You may find it a little stifling at first, but it is most necessary." Both put on the masks, after which Drost handed the Count a pair of rubber gloves. These Ortmann put on, watching Drost, who did the same. "It is a good job, Count, that we are alone in the house, otherwise I could do no work. The gas is heavy, and any escaping from here will fall to the basement. One fourteen-thousandth part in air, and the result must be fatal. There is no known antidote. Ah!" he laughed, "these poor, too-confiding English little dream of our latter-day discoveries--scientific discoveries by which we hold all the honours in the game of war." "Very well," grunted the Count. "Let us hope that our science is better than that of our enemies. But I confess that to-day I have doubts. These British have made most wonderful strides--the most amazing progress in their munitions and devices." While he spoke old Drost was, with expert hand, mixing certain compounds, grey and bright-green crystals, which he pounded in a mortar. Then, carefully weighing with his apothecary's scales several grammes of a fine white powder, he added it and, while the Count, still wearing his ugly mask, watched, mixed a measured quantity of water and placed the whole into a big glass retort which was already in a holder warmed by the pale-blue flame of a spirit-lamp. Suddenly Drost made a gesture to his companion, and while the liquid in the retort was bubbling, he attached to the narrow end of the retort an arrangement of bent glass tube, and proceeded to distil the liquid he had produced. This product, which fell drop by drop into a long test-tube, was of a bright-blue colour. Drop by drop fell that fatal liquid--fatal because it gave off a poison-gas against which no human being could exist for more than five seconds. "This," exclaimed Drost, his voice muffled by his mask, "is the most fatal of any gas that chemical science has yet discovered. It does not merely asphyxiate and leave bad symptoms afterwards, but it kills outright in a few seconds. It is absolutely deadly."