The man fell to the ground without a sound.

Frank, advancing upon the other German, also was challenged when he drew close, but he, too, engaged his prey in conversation. As the man turned his head for a moment to gaze across the dark sand, the lad struck him violently over the head with his revolver b.u.t.t. The German dropped like a log.

A few moments later Frank and Jack met again near the first aeroplane.

"It'll have to be quick work here," Jack warned "We haven't a whole lot of time, you know."

Frank nodded that he understood. Rapidly they pa.s.sed from one plane to another letting out the gasoline. Five minutes later, with the exception of their hydroplane, which rested some distance away, every craft upon the beach was dry. They were absolutely useless--or so the lads thought.

"Now for the papers," said Jack, as he straightened up after tinkering with the last machine.

Cautiously the two lads advanced upon the sleeping German. Frank raised his revolver and would have brought it down on the man's head had not Jack stayed him with a gesture.

"No need of that," he said. "I don't like to hurt a man except when it is absolutely necessary."

Frank put the revolver back in his pocket.

Gently, Jack thrust his hand into the German's pocket. He fumbled about a moment and then drew forth a paper. Turning his head aside he struck a match and glanced at the paper. Then he nodded his satisfaction.

"This is it," he said.

Frank, at that moment, had risen to his feet. Believing the work was accomplished, he was moving off toward the hydroplane. As Jack now made to get to his feet, he chanced to glance at the German he had just relieved of the papers.

The lad uttered an exclamation of surprise, and no wonder. The man's eyes were open and gazed straight at Jack. In his hand he held a revolver and it was levelled at Jack's head.

"Hands up!" said the German, quietly.

There was nothing for Jack to do but obey or be shot. His hands went high in the air, but he still retained the valuable papers.

"Drop those papers," was the next command.

Jack obeyed and the papers fluttered to his feet. The German reached out and picked them up with his left hand while with his right he still covered the lad with his revolver.

"So you're a spy, eh?" said the German.

Jack made no reply, but a gleam of hope lighted up his eye; for, Frank, chancing to turn for some unexplainable reason, had taken in the situation and was now advancing on tiptoe to his friend's aid.

"How did you get here?" demanded the German, making ready to rise.

Again Jack made no reply; but none was necessary, for at that moment Frank had come within striking distance. His arm rose and fell, and as his revolver b.u.t.t descended upon the German's head, the latter toppled over in a heap.

Quickly, Jack stooped and again recovered the papers he had taken so much pains to get.

"Come on!" cried Frank. "We haven't time to fool around here. The rest of this crowd is likely to wake up in a minute or two."

Jack followed his friend across the sand. They laid hold of the hydroplane and rolled it toward the water. In it went with a splash and Frank cried:

"Climb aboard quickly!"

Jack needed no urging and a moment later the two boys were ready for flight. And then, suddenly, there was the crack of a revolver behind them and a bullet flew close to Jack's ear.

The German leader had recovered consciousness, and springing to his feet, dashed to the water's edge and fired point blank at the machine.

Fortunately, in his excitement his aim was poor and he missed. Before he could fire again, Frank wheeled about and his revolver spoke sharply.

The German threw up his arms, and with a gasp, pitched headlong into the sea.

But the sounds of the two shots had aroused the sleeping camp. Wild cries came from the sh.o.r.e, followed by heavy footfalls as the Germans rushed toward the water.

"Hurry, Frank!" cried Jack.

As lightly as a fairy the hydroplane skimmed over the water; then went soaring in the air. Frank gave a loud cheer.

"Safe!" he exclaimed.

But the lad was wrong.

From on sh.o.r.e came a chorus of angry cries and imprecations. Hastily the Germans made a rush for their aeroplanes to give chase. None would move. Followed more cries and angry shouts.

"Wait," said one German. "I've some gasoline."

Rapidly he opened up a big can, which he took from the bottom of his machine. Quickly the tank was filled and the man climbed into the pilot's seat. Another jumped in with him.

"Give us some of that gasoline!" cried another.

The German shook his head.

"Not enough," he replied. "We'll overtake those fellows and then come back for the rest of you."

The aeroplane leaped skyward and started in pursuit of Frank and Jack.

The two boys, believing that they were safe, were going along only at a fair rate of speed when Jack's keen ears caught the sound of the pursuing machine.

"They're after us, Frank!" he called.

"Impossible!" replied Frank. "How can they fly without gas?"

"Well, they're coming, all the same," declared Jack.

He produced his two revolvers and examined them carefully.

"You run this thing and I'll do what fighting is necessary," he said.

"Wish I could shoot like you can; but I can't; and I can't run this machine either."

The German aeroplane was gaining steadily.

"He can outrun us," said Frank, quietly. "There is only one, thank goodness. You'll have to bring him down, Jack."

"I'll try," was Jack's reply. "If I had a rifle I might be able to pick him off now."