As he rested, he heard the murmur of a skyplane's motors and turned to behold a giant Gotha machine heading up the coast. Stretching himself out quickly, as though to simulate the posture of a drowned man cast up by the waves, he lay wide-eyed watching the German birdman. Undoubtedly, it was one of the aerial coast patrol. Five hundred feet above, it lazily floated along. It came closer and closer, finally flying almost directly overhead. With bated breath the boy on the sand waited for its passage and heaved a great sigh of relief as it purred onward in the direction of Blankenberghe without giving any indication as to whether its pilot had noted the body on the sand below. Jack scrambled to his feet. "Might as well find out what's doing here," he muttered to himself. He peeled off his wet clothes. One at a time he wrung out his garments and shook the water out of his long black hair. Then he turned for a glance around him. In front of him loomed the sand dunes, their weird shifting formations dotted here and there with scraggly underbrush. Down the coast the picture was the same. Turning, the lad gazed northward in the general direction where he knew lay Holland and her neutral shores. "That's where I go from here," he said cheerfully. He had jogged along not more than a quarter of a mile when the coast line veered sharply to right, leaving only the expanse of ocean looming up beyond the stretch of sandy beach. Following along the curve in the coast line, Jack found himself presently on the shore of a small land-locked bay. The mouth of the inlet was barely wide enough to permit the passage of a good-sized vessel. But neither ship nor human being was in sight. "Might be one of the secret passageways used by the undersea boats," Jack mused as he followed the curving line of the bay away from the ocean. Presently he came to an abrupt halt at a break in the beach where the rolling sand dunes fell sheer away to the mouth of another waterway---this time a small stream that wound its way inland through a tortuous channel. It was no more than two hundred feet across. Jack realized this must be one of the canals with which the coast was known to be ribboned. For a moment he stood in contemplation of the sight. Now he was more than ever convinced that he had stumbled into a U-boat base. The love of adventure gripped him and he determined to press on. For the next ten minutes he threaded his way along the canal bank. Suddenly, as he turned one of the snake-like twists in the course of the waterway, he found himself facing an old stone windmill that stood almost directly on the canal bank. It was only a stone's throw away. Instinctively the boy threw himself upon the sandy loam. There was not a sign of life about the abandoned structure. In the peaceful days before the war it had, no doubt, been used by a Belgian farmer to water his fields.