as sure as
anything," breathlessly admitted the second watcher.

"No fellow would act that way unless he wanted to keep from being seen,
would he?" asked Harry.

"You're right there. Oh! I saw a second one follow him then, Harry!"

"Yes, there's a pair of the creepers. That makes me believe more than
ever they were aboard one of those bombing planes, Tom."

"It might be they fell when one of the Hun raiding planes was knocked
out," suggested the other, as an idea struck him. "Only one went down in
flames, I remember now. Those in the other may have managed to make a
safe landing, and bent on hitting us a crack before trying to get back
to their lines, they've crept into the camp here."

"Carrying some grenades, I'd like to wager, which they can use in
kicking up a big row, under cover of which they'll scoot off," Harry
went on.

"We must put a peg in their plans then," whispered Tom. "It'd be a shame
to let them do what their pilots failed in, and blow up a part of our
hangar field here."

"If they do they'll go up with the planes then!" Harry gritted between
his set teeth. "Come, let's move on and corner the Huns!"

This suited Tom. Discretion might have caused them to alarm the camp and
in this way cause the prowlers to disappear. But ambition, on the other
hand, had fired the hearts of the two boys. They saw an opportunity to
get in a telling blow by capturing those two spies. It was a chance to
gain a little fresh glory, as well as to protect the monster plane of
Beresford.

Accordingly they commenced to move forward, bending low and taking
advantage of every dense shadow that came in their way. Their objective
was the hangar that afforded shelter during the night to the novel and
as yet untried monster plane, of which so much was expected, and rumors
concerning which might have even sifted into the enemy lines.

Of course both Tom and Harry were keenly on the alert for the first
fresh sign of the prowling enemy, whose designs they had set out to
balk. Very probably the Huns would resist desperately, and there might
be a fight. Tom felt his heart beat tumultuously, but such a thing as
fear did not enter into his calculations.

CHAPTER XII

A LIVELY CHASE

"THEY'VE gone," presently whispered Tom, in a disappointed tone.

"Only hiding somewhere near by," Harry assured him, equally careful to
lower his voice. "We'll begin to circle around, and presently rout them
out. Be ready to jump the firs