They crawled along through the black suffocating darkness, feeble, languid, and sweating at every pore. There was a murky closeness in the vitiated atmosphere that seemed to take all the strength and energy away. At any other time the walk to Clarence Terrace would have been a pleasure, now it was a penance. They found their objective after a deal of patience and trouble. Hackness yelled in the doorway. There was a sound of footsteps and Cynthia Grimfern spoke. "Ah, what a relief it is to know that you are all right," she said. "I pictured all sorts of horrors happening to you. Will this never end, Martin?" She cried softly in her distress. Hackness felt for her hand and pressed it tenderly. "We are going to try my great theory," he said. "Eldred is with me, and we have got Williamson's permission to operate with the aerophane. Where is Sir Edgar?" Grimfern was in the big workshop in the garden. As best he could, he was fumbling over some machinery for the increase of power in electric lighting. Hackness took a queer-looking lamp with double reflectors from his pocket. "Shut off that dynamo," he said, "and give me the flex. I've got a little idea here Bramley, the electrician, lent me. With that 1000-volt generator of yours I can get a light equal to 40,000 candles. There." Flick went the switch, and the others staggered back with their hands to their eyes. The great volume of light, impossible to face under ordinary circumstances, illuminated the workshop with a faint glow like a winter's dawn. It was sufficient for all practical purpose, but to eyes that had seen absolutely nothing for two days and nights very painful. [Illustration: The great volume of light, impossible to face under ordinary circumstances, illuminated the workshop with a faint glow.] Cynthia laughed hysterically. She saw the men grimed and dirty, blackened and greasy, as if they were fresh from a stoker's hole in a tropical sea. They saw a tall, graceful girl in the droll parody of a kitchen-maid who had wiped a tearful face with a blacklead brush. But they could _see_. Along the whole floor of the workshop lay a queer, cigar-shaped instrument with grotesque wings and a tail like that of a fish, but capable of being turned in any direction. It seemed a problem to get this strange-looking monster out of the place, but as the whole of the end of the workshop was constructed to pull out, the difficulty was not great. This was Sir Edgar Grimfern's aerophane, built under his own eyes and with the assistance of Hackness and Eldred. "It will be a bit of risk in the dark," Sir Edgar said thoughtfully. "It will, sir, but I hope it will mean the saving of a great city," Hackness remarked. "We shall have no difficulty in getting up, and as to the getting down, don't forget that the atmosphere a few miles beyond the outskirts of London is quite clear. If only the explosives are strong enough!"