For nearly an hour he toiled diligently, until the sweat poured down his face in spite of the cold blast of air through the opening. But the effort was in vain. It was the blade of his knife that was diminishing, not the cement, which was as hard as cast iron. "I'll knock off, sir," he said, scratching his head in his disappointment. "Might go on for a whole month of Sundays, and yet get no forrader." "We'll try to get those bars red-hot," declared Fordyce. "We've plenty of wood. Once we get the iron soft we can knock them out by using a log as a maul." "Might be done, sir," admitted Chalmers. "No harm in trying; it'll keep us out of mischief, in a manner of speaking." Acting upon the Sub's suggestion, a quantity of wood was stacked between the bars and set on fire. Fanned by the strong air-current, the combustibles burned fiercely, but the result was far from satisfactory. In less than five minutes the cellar was filled with choking fumes, and had not the experimenters torn away the burning wood they would have been suffocated. [Illustration: IT WAS MINDIGGLE] The hours passed slowly. Hunger and want of sleep were beginning to assail the prisoners. For their personal comfort they kept the big heating-stove well supplied, as they had not the slightest fear that a fall in temperature would affect the contents of the dummy packet which Fordyce still retained. The two men were almost on the point of falling into a fitful slumber when Klostivitch's voice hailed them. Lighting the lamp, Fordyce made his way to the passage. A sense of dignity forbade him to hurry, but curiosity prompted him to ascertain the cause of the interruption. The place was deserted. The Russian had removed the stone covering to the trap, for on the floor was a basket containing food and a jar of water. "He evidently doesn't mean to starve us," commented the Sub as he carried the basket to the cellar. "I wonder if the stuff's drugged." "I'll risk it, anyway," declared Chalmers. "I'm fair famished, sir. How goes the enemy, sir?" Fordyce consulted his watch. "A quarter-past nine," he replied. "You turn in, Chalmers. I'll take first trick." The petty officer, having eaten his share of the scanty repast, was soon sound asleep. Fordyce, having made up the fire, prepared to keep watch, not knowing what move his captor might make. It was close on midnight when he heard his name called. Hardly able to credit his senses, the Sub started to his feet. The voice seemed familiar, yet he could not fix the speaker's identity. Relighting the lamp, and without disturbing his sleeping companion, the Sub hastened along the passage. Suddenly he halted. The trap-door above his head was opened, and through the aperture could be seen the head and shoulders of a man. His features were muffled in a turned-up fur collar, while an astrakhan cap was drawn well down over his forehead; but, in spite of this, Fordyce was now able to recognize the man. It was Mindiggle. CHAPTER XXIV