Beale's eyes followed the benches and took in every detail. Some of the men were evidently engaged in tests, and remained all the time with their eyes glued to their microscopes. Others were looking into their porcelain trays and stirring the contents with glass rods, now and again transferring something to a glass slide which was placed on the microscope and earnestly examined. Beale was conscious of a faint musty odour permeating the air, an indescribable earthy smell with a tang to it which made the delicate membrane of the nostrils smart and ache. He tied his handkerchief over his nose and mouth before he took another peep. Only part of the room was visible from his post of observation. What was going on immediately beneath the far side of the screen he could only conjecture. But he saw enough to convince him that this was the principal factory, from whence van Heerden was distilling the poison with which he planned humanity's death. Some of the workers were filling and sealing small test-tubes with the contents of dishes. These tubes were extraordinarily delicate of structure, and Beale saw at least three crumble and shiver in the hands of the fillers. Every bench held a hundred or so of these tubes and a covered gas-jet for heating the wax. The work went on methodically, with very little conversation between the masked figures (he saw that the masks covered the heads of the chemists so that not a vestige of hair showed), and only occasionally did one of them leave his seat and disappear through a door at the far end of the room, which apparently led to a canteen. Evidently the fumes against which they were protected were not virulent, for some of the men stripped their masks as soon as they left their benches. For half an hour he watched, and in the course of that time saw the process of filling the small boxes which formed his barrier and hiding-place with the sealed tubes. He observed the care with which the fragile tubes were placed in their beds of cotton wool, and had a glimpse of the lined interior of one of the boxes. He was on the point of lifting down a box to make a more thorough examination when he heard a quavering voice beneath him. "What you do here--eh?" Under the step-ladder was one of the workers who had slipped noiselessly round the corner of the pile and now stood, grotesque and menacing, his uncovered eyes glowering at the intruder, the black barrel of his Browning pistol covering the detective's heart. "Don't shoot, colonel," said Beale softly. "I'll come down." CHAPTER XXV THE LAST MAN AT THE BENCH After all, it was for the best--van Heerden could almost see the hand of Providence in this deliverance of his enemy into his power. There must be a settlement with Beale, that play-acting drunkard, who had so deceived him at first.