"Is it a--mine?" he cried sharply. The Prince shook his head. "There would be nothing of us left at this moment," he said. "Wait! You can feel the steady throb of the engines. No, it was a gun. It was a bursting shell from one of the silent guns. They can see our periscope, and are firing across us--to heave to. Hark! There goes another." Again came a terrific detonation. But the vessel ploughed on. "Presently they will fire to hit our periscope and make us rise to the surface. Von Salzinger has gone further than I had dared to hope." "Hope?" "He will pay for this with his position." "But if they hit our periscope?" The Prince shrugged. "It will make no difference. We shall not rise till it suits us. We have the light. Already we must be nearly through the mine-field. Once we are through the mines Ludovic could make the journey seawards blindfold." The Prince crossed over to his chair, and laid the sealed rolls on the table beside him. He did not speak. He was obviously listening. Presently another sharp explosion sounded overhead, and his eyes lit. "Ah, I thought Von Salzinger would not resist it. You see, he is a Prussian." He smiled, but his eyes had lost their humor. "That was shrapnel," he went on. "Its bursting is unmistakable. But he will not hit the periscope." Again silence fell between them, and both smoked on with every sense alert. There was another explosion overhead. Then another and another. Still the vibrations of the engines continued. The two waited some time for the next explosion, but it was delayed. At last the Prince rose from his seat and passed out of the room. He was away for some moments. During his absence Ruxton never stirred a muscle. His cigar had gone out. He was still listening acutely. Finally the Prince returned, and Ruxton's eyes put their question plainly. "We have completely passed the mine-field. We are also completely submerged," said the Prince. "We need no longer concern ourselves with Von Salzinger." Ruxton drew a deep breath. He relit his cigar, while the other seemed to dismiss the subject from his mind entirely. The excitement of the escape had passed, and with the passing of it, it had robbed him of all lightness. His large eyes darkened, and a frowning of his bushy brows gave him an appearance of depression. Ruxton, watching him, wondered what next was to be the display of this extraordinary creature. Nor had he long to wait. "You have seen at--Borga?" he demanded. "More--than I was prepared for, in spite of all you and the Princess had told me." "Yes. Tell me. Tell me about it." Ruxton drew his feet up on the lounge. His dark eyes were on the white-whiskered face of his host, but they had become deeply introspective. "I wonder how many years we have before it--comes." "Perhaps--ten."