He was within a few feet of the disabled craft and he now rose higher in the water to get a good look about. Still he saw no one. Twice around the machine the lad swam and not a human being did he see. "There is something awfully queer about this," he told himself. "I'll go aboard." He laid hands on the aeroplane and scrambled aboard. Quickly he sprang to his feet, ready to tackle any foe that might have seen him crawl aboard. Nothing happened. Jack made a careful inspection of the disabled plane. Then, as he still gazed around, a sudden thought struck him. Without taking time to consider it, he sprang suddenly to the side of the plane and leaped into the water and with swift and powerful strokes struck out for his own craft. Jack had hit upon the solution of the desertion of the German aeroplane. Even as Jack had lowered himself from the hydroplane and swam across the water, the Germans in the other craft had done the same thing. Both sides had struck the same plan almost simultaneously. Jack, in making a wide detour as he approached the foes' machine, must have passed the two Germans in the water. Now, realizing that the Germans must be close to the hydroplane, had they not already reached it, and remembering that Frank was wounded, Jack felt a sudden dread steal over him. His long, powerful strokes sent him through the water at great speed. But the Germans had not made their presence known to Frank yet. Neither was as swift a swimmer as Jack, and for that reason, their progress through the water had been considerably slower. Also they had gone very cautiously. A short distance from the hydroplane, one had swum to one side of the plane and the second to the other. The Germans also had discarded their revolvers, for they had realized they would be useless after their trip through the water. Also, not being expert swimmers, they had wanted to be unhampered by weight as much as possible. Frank was still guiding the plane about occasionally to avoid a chance bullet from the enemy, but at the moment the Germans came close, he had stopped the craft and was peering into the darkness, straining his ears for the sound of a struggle that would tell him Jack was engaged with the enemy. Suddenly a sound came to his ears from across the water, but it was not what he expected, although it was in Jack's voice: "Frank! Look out! They are after you!" Instantly, the lad understood the situation. He drew his revolver with his uninjured arm and sprang to one side of the aeroplane. As he did so, a figure reached up and grabbed him by the hand so that he could not fire. At the same time a second figure clambered aboard the craft from the opposite side. Frank raised a cry: "Hurry, Jack!" Jack needed no urging. He was swimming through the water as fast as possible.