"Make your elevation half a mile and then head west, slowly. The chances are there will be more of them. In the darkness we can let them overtake us and mingle with them in safety." Frank gave his endorsement to this plan and the machine continued to rise. At the proper elevation, Frank turned the hydroplane's head westward and reduced the speed to less than thirty miles an hour. So slow was its gait, in fact, that it had the appearance of almost standing still. Jack scanned the eastern horizon with his glass. "See anything?" asked Frank. "Thought I did," was the reply, "but whatever I saw has disappeared now. Guess I must have been mistaken." But Jack had not been mistaken. Far back, even now, a fleet of perhaps a dozen German air planes were speeding westward. For the most part they were small craft, having a capacity of not more than three men, with the single exception of one machine, which, larger than the rest, carried four men. The air planes were strung out for considerable distance, no two being closer than two hundred yards together. And in this manner they overtook the hydroplane driven by Frank and Jack. Jack, again surveying the horizon with his night glass, gave an exclamation. "Here they come, Frank," he said. "Let her out a little more." Frank obeyed without question and the speed of the hydroplane increased from something more than thirty miles an hour to almost sixty. And still the Germans gained. "This will do," said Jack, leaning close to Frank. "They'll overtake us, but believing we are of their number, there is little likelihood that they will investigate us very closely. We can fall in line without trouble and accompany them wherever they go." "Suits me," said Frank. "Just keep me posted on their proximity." Gradually the Germans reduced the distance and at length the first plane was only a few yards behind the craft in which Frank and Jack were risking their lives. The German craft flashed by a moment later without paying any attention to the hydroplane. "Little more speed, Frank," called Jack. The hydroplane skimmed through the air faster than before and the next German craft did not overtake it so easily; but at length it passed, as did a third and a fourth. "Here's a good place for us to fall in line," Jack instructed. Again Frank increased the speed of the hydroplane and it moved swiftly in the wake of the fourth German craft. After that no enemy air plane passed them. "Any idea where we are?" asked Frank of his chum. "We're not far off the Belgian coast, but how far west I can't say," returned Jack. "Don't suppose it makes any particular difference, though." "I guess not." Frank became silent and gave his undivided attention to keeping the German plane ahead of him in sight. And in this manner they proceeded for perhaps another half hour. Then the machine ahead of Frank veered sharply to the south. Frank brought the head of his own craft in the same direction and the flight continued.