er the land,
a sudden bombardment broke out from the German air planes.

It was not the sound of bombs that came to the lads' ears; rather the
sharp "crack! crack!" of revolver firing. Jack and Frank gazed about
them quickly, for they believed, for the moment, that the Germans had
encountered a squadron of French airships.

But there was no other machine in sight save the German craft.

"What in the world is the meaning of this?" Frank asked of Jack.

"Don't know," returned the lad, "but I guess I'd better join in."

He drew his revolver and fired several shots in the air.

"Seems to be expected of us," he said. "We don't want to disappoint
them."

The German aircraft now headed straight for the city of Calais. Frank
sent his machine speeding in the same direction. Then, just as it
appeared they would fly directly above the city, the first German craft
began to descend. The others did likewise and a moment or so later they
all came to earth in the center of what Frank and Jack could see was a
small army camp; and as they alighted from their machines, the lads saw
that it was an Allied camp and not a German.

"Must be Calais," said Frank to Jack in a whisper. "Have we been
mistaken? Are these French and British machines?"

"Well, it looks like it," returned Jack. "We'll keep quiet and let the
other fellows do the talking."

A French officer now approached the pilot of the first aircraft.

"We heard the firing aloft a moment ago," he said. "Did you encounter
the enemy?"

"We were pursued all the way from the German lines," was the reply.

"Anyone hit?"

"I think not, though I believe we accounted for one or two of the
enemy."

"Good. Will you fly again tonight?"

"Yes; but not before midnight."

The French officer withdrew.

At this one of the aviators raised a hand and the others gathered about
him, Frank and Jack with them. All wore khaki clothing and their
features were concealed by heavy goggles.

"Careful," whispered the aviator. "A false move and we are discovered.
Spread out now and see what you can learn. Gather here at midnight."

He waved a hand and the Germans, for such Jack and Frank now knew them
to be, separated. When the two lads were alone a moment later, Jack
said:

"Well, this is what I call a piece of nervy business. What shall we do?
Inform the French commander immediately?"

"No. I have a better plan that that. They can hardly work any mischief
tonight. What information th