"I knew I ought to recognize that sound!" said Fred.
It seemed fairly safe for them to speak to one another now. For some reason it was quite evident they had been forgotten.
There was an interval of almost complete silence; then came a sudden explosion of orders. Half a dozen motorcycles sprang into crackling life; there was the unmistakable din of a powerful aeroplane engine, which, with no muffler, is noisy enough to wake the dead. Then came the whirring of its propeller. They were sure that if they only dared to raise their heads, they would see the machine rising near by.
But there was more to follow that was just as inexplicable. The motorcycles chugged away; then three automobiles started. Their engines roared for a moment before they subsided to the ordered, steady hum of a smooth running motor. On the first car that got away there was a horn that made Boris start convulsively as he heard its bugle note, and grasp Fred's shoulder.
"That horn belongs only to a car used by a full general!" he said. "It must be von Hindenburg going, Fred! That flying machine brought important news!"
That had been evident to Fred almost from the first. He wondered mightily what was going to happen next. It seemed incredible that the Germans, knowing that he and Boris must soon be found, and that only patience was necessary if they were to be caught, would so quickly give up looking for them. And yet—Boris was right, of course. A general would not depart with such abundant evidence of haste and sudden decision unless some grave news had come through the air.
One question was soon settled. Scarcely had General von Hindenburg's car started, with the musical call of its horn clearing the way for it, when the search for the two scouts was renewed with as much vigor as had been shown before the coming of the aeroplane. And this time it was speedily successful. There was less din and confusion. Fred saw at once that some officer with a cool and level head had taken charge. The searchers now did the simple, obvious thing. They divided the grounds up into sections, and beat over each section thoroughly, with the result that a corporal and a private speedily came upon Boris and Fred, and, raising a sort of view halloo, dragged them out into the open, flashing their electric torches in their eyes.
"Here they are!" cried the corporal. "Herr Hauptmann, here they are!"
A captain came up quickly, and at the sight of Fred exclaimed sharply in his surprise.
"You're the boy I chose to help with the work in the house here!" he said. His face darkened. "He is a spy! Take him into the guard room and lock him up." He barely glanced at Boris. "Yes, that is the other. See that he is taken back to his quarters, corporal, and that a sentry remains constantly on guard."