The door was closed, and a knock brought no response. One of the soldiers burst in the door with the toe of his boot and all entered. They ransacked the place from top to bottom, but could find no one. "When they came back and found the storekeeper bound, they released him and all moved," said Frank. "That's about the size of it," Jack agreed. "They knew when they found him that their rendezvous had been discovered." "They have left no clue," said the Russian officer in command, "so there is nothing to be done. Come, we shall go." They returned to the palace, where the Czar insisted on having Lord Hastings, Frank and Jack dine with him. This they did, and at a late hour returned aboard the D-16. "And which way shall we go now?" asked Frank. "Well," said Lord Hastings, "I had thought of going back the way we came." "Suits me," said Jack. "Of course there is considerable action over here, but I am not particularly fond of the brand. I would rather get back on the other side." "As long as we are practically free agents," said Frank, "I have a plan to propose." "And that is?" asked Lord Hastings. "Well, it probably will be weeks before the allied ships are able to force a passage of the Dardanelles, and with our speed, we can reach there long before that. See what I mean?" Lord Hastings smiled. "I see," he replied briefly. "And what do you think of the plan?" "I am in favor of it," said Jack. "And so am I," declared Lord Hastings. "But, remember, to get there quickly we shall once more have to pass through the Kiel canal." "We did it once. We can do it again," replied Frank quietly. CHAPTER XXI. A NEUTRALITY VIOLATION. Through the Gulf of Finland into the Baltic the D-16 made her way rapidly, remaining upon the surface of the water, for in these seas there was no danger of encountering an enemy. Some miles from the mouth of the Kiel canal, however, Lord Hastings gave the command to submerge, and the little submarine, sinking gently, hurried on, at a somewhat reduced speed, but making good time nevertheless. On this second passage of the canal, Lord Hastings decided to make no raid upon the enemy's fleet cooped up within it, and accordingly the D-16, running close to the bottom, guided by Lord Hastings' own hand, made the trip in safety, without encountering a single one of the enemy's under-the-sea fighters. However, she did not rise immediately when she was once more in the North Sea, for these waters were mined for miles, and it was necessary for the D-16 to pass under the mined area before coming again to the surface. But, going more swiftly now, the British submarine soon reached a zone of comparative safety and Lord Hastings gave the command to come to the surface once more. Then, followed by Frank and Jack, he stepped on to the bridge for a breath of the cool air.