men. To the north,
to the south, and to the east and west the dense mass of humanity
stretched out. Hal and Chester, flying close to the earth, at last could
make out moving forms below them.

Suddenly it became light. Not broad daylight, but the darkness gave way
enough for the lads to distinguish what lay below them. The dawn of
another day was breaking.

At the same instant that the lads made out the huge mass of humanity
upon the ground their presence in the air was discovered. There came the
sound of a single shot and the whiz of a bullet, as it sped close to
Hal's ear.

With a quick movement the lad sent the plane soaring high in the air
once more. So sudden was the movement that Chester, caught unprepared,
lost his balance, and saved himself from tumbling to the ground only by
clutching the side of the machine. Marquis also had a narrow escape from
being thrown out. He let out a loud yelp of fear, as he was thrown
violently against Chester. The lad threw out a hand and grabbed him by
the scruff of the neck, just as it seemed he would plunge to certain
destruction.

"Say!" he called to Hal, when he finally regained his breath and his
head. "What's the matter with you? You almost dumped us both out."

"Did I?" replied Hal briefly. "Well, as long as you didn't fall it's all
right. We had to come up suddenly, or the chances were we would have
gone down suddenly. But it's my fault. I should have given you warning.
Are you hurt?"

"No," replied Chester.

"I'll be careful next time," said Hal. "You'll have to forgive me this
once."

"Say no more about it," answered Chester. "But what was the cause of
this sudden rise?"

"Cause!" repeated Hal in astonishment. "You don't mean to tell me you
don't know the cause? Didn't you hear that shot?"

"Yes, I heard it. But how do you know whether it was fired by friend or
foe?"

"I can't see as that would make any difference if it happened to hit us.
However, I'm morally certain they were Germans."

"Well, maybe they were. What are we going to do now?"

"We'll stay up here until we are absolutely certain we have passed over
the German lines. Then we'll come down."

The machine was high in the air now, and, peering intently over the
side, as he did, Chester was unable to make out anything below in the
early morning light.

But in the rear, soaring high in the air, although neither lad realized
it, a new danger threatened. When the presence of the boys' plane had