"We'll plant it alongside the gun--No, we'll get into their working underground. We'll blow their equipment into scrap-iron, and perhaps we can even damage the gun itself!" He was almost beside himself with excitement at thought of a weapon being placed in his straining helpless hands. * * * * * It was the earth-shaking thunder of the big gun that hastened their final preparations and made McGuire tremble with suppressed excitement where he helped Sykes to draw off a syrupy liquid into heavy crystal flasks. There were many of these, and the two men would allow no others to touch them, but stored them themselves and nested each one in a soft bed within the submarine. Then one last repetition of their half-formed plans to Djorn and his followers and a rush toward the wharf where the submarine was waiting. Althora was waiting, too, and McGuire wasted minutes in a petition that he knew was futile. "Wait here, Althora," he begged. "I will come back; this is no venture for you to undertake. I can take my chances with them, but you--! It is no place for you," he concluded lamely. "There is no other place for me," she said; "only where you are." And she led the way while the others followed into the lighted control room of the big under-water craft. McGuire's eyes were misty with a blurring of tears that were partly from excitement, but more from a feeling of helpless remonstrance that was mingled with pure pride. And his lips were set in a straight line. The magnetic pull that held them to their anchorage was reversed; the ship beneath them was slipping smoothly beneath the surface and out to sea, guided through its tortuous windings of water-worn caves and rocky chambers under the sea by the invisible electric cords that drew it where they would. And ahead on some mysterious island was a gun, a thing of size and power beyond anything of Earth. He was going to spike that gun if it was the last act of his life; and Althora was going with him. He drew her slim body to him, while his eyes stared blindly, hopefully, toward what the future held. CHAPTER XVI Throughout the night they drove hour after hour at terrific speed. The ship was running submerged, for McGuire was taking no slightest chance of their being observed from the air. He and the others slept at times, for the crew that handled the craft very evidently knew the exact course, and there were mechanical devices that insured their safety. A ray was projected continuously ahead of them; it would reflect back and give on an indicator instant warning of any derelict or obstruction. Another row of quivering needles gave by the same method the soundings from far ahead. But the uncertainty of what their tomorrow might hold and the worry and dread lest he find himself unable to damage the big gun made real rest impossible for McGuire.