On the following morning Lawless noticed that the _Black Diamond_ left her berth and steamed down the river about an hour before the _Mars_ and her escort were due to leave. "Well, your nightmare's ship's gone now," remarked Trent. "One of the port officials told me she had cleared for Valencia with coals." "Coals!" echoed Lawless. "Rum sort of place to ship coals for the Mediterranean! They could get it cheaper and quicker at Cardiff and Newport, besides saving about four days on the double trip." Soon afterwards came the signal to get under way. The _Mars_ was to proceed at about ten knots, with the _Arrow_ and _Kite_ astern on each side, and the _Knat_ in front to act as scout and clear the way for her. Slowly and majestically the marine monster--the latest triumph of death-dealing mechanism--swung down the river, her convoy of destroyers looking no larger than midges against her huge bulk. Evening was drawing in as they came abreast of the white light on Cambrae Island, and, although he had been keeping a careful look-out all the afternoon, Lawless had seen nothing of the mysterious _Black Diamond_. "It's strange!" he mused. "I can't understand it." An hour or two later, when darkness had set in, Lawless left Trent in charge and went below to snatch a little rest. He had hardly been in his bunk ten minutes, when a messenger knocked at the cabin door and informed him that he was wanted on the bridge. "What's the trouble?" asked the Lieutenant, as he reached the bridge. Trent withdrew his head from the hood-screen on the port side, and pointed to a couple of vertical red lights some distance ahead. "Steamer broken down," he said; "thought it might be your bogey ship." Lawless picked up the night glasses and gazed through them for some moments. "It's the _Black Diamond_, right enough," he said. "Queer she should have a mishap right in our course, though!" Trent laughed scornfully. "I don't suppose they're hanging about there for fun," he observed. "If they were really up to any games, they wouldn't show the warning lights." "That's just it," replied Lawless. "They know it would at once excite suspicion if they didn't show them." And he again studied the vessel through his glasses. "Trent," he exclaimed suddenly, "did you see anything?" The junior officer, although he had been gazing in the same direction as Lawless, had seen nothing of a startling character. "No," he replied. "What was it?" "I'll swear I saw something slipped overboard," said Lawless; "but it's so dark I couldn't see what it was even with these glasses. Look here," he added, with unusual gravity, "there's some mischief going on. I'm certain of it." "Then we'd better have the searchlight on her," replied Trent; and was about to give an order when the Lieutenant stopped him. "No," he said decisively, "that would only serve to warn them if they are up to any artful dodges."