It was finally given, and Roque directed immediate descent. On the ground once more, Billy and Henri relapsed into their dutiful service as "sons" and rear guards of the renowned "Dr. Blitz." The glazed caps had gone the way of the winds, but, as Billy put it, "we are still dressed up to beat the band." The boys noticed that, barring a few skilled workmen and engineers, they were the only civilians in the streets that evening. They did not count Roque, for he might turn out to be a general, if occasion served. The latter had a busy hour with the garrison officers, while the boys had an idle one, with about as much activity as is allowed a hobbled horse. It was evident that "Dr. Blitz" held this island as a holy of holies, secret even to his "sons." "It beats me," observed Billy, edging away as far as possible from the guard stationed to keep them out of mischief, "how those Britishers ever got by this place." "The bigger question," asserted Henri, "is, if they got by, how in the world did they ever get back?" "That's what Roque is evidently trying to find out," intimated Billy. The boys, while puzzling over the problem of "get by and get back," were looking at the huge fortress so tremendously fortified and noting everywhere an uninterrupted view of the sea. They also surmised that an alert garrison was ever carefully watching the waters, day after day, night after night, hour after hour, in order not to be surprised by the powerful enemy. "I guess the fog helped some," was the conclusion finally advanced by Billy. "And Ardelle somewhere behind the curtain," suggested Henri. "Oh, go 'way, man; Roque has given you the Ardelle fever." Billy just then caught sight of Roque bearing down upon them under full stride. "Speak of the dickens," he exclaimed, "here he comes now." The shadows of evening continued to gather, and here and there on the island lights showed like glowworms. Roque shook hands with his officer companions. He evidently contemplated leaving in the same impetuous way that he came, but evidently not by the seaplane route. A little steam launch tugged at its holding rope, in readiness to dash away into the misty deep. Two men muffled to the throat waited the order. Roque, with never a word to the boys, directed them by gestures to get aboard, quickly following. The launch cut through the now pitchy darkness of the Helgoland waters. With the island lights no longer visible, there could only be seen the lantern in front of the little boat, and it was a dangerous speed to be making, when the helmsman had scant view of hardly a yard ahead. But the man at the wheel was in familiar element, to him, and the scudding vessel never came to drift movement until a glimmering signal guided to the landing place, the name of which would have meant nothing to the boys if they had had the care to inquire. This was Christmas night in the Bight of Helgoland. CHAPTER III. A THRILLING MOMENT.