did a bungling bit of work, and the cylinders have
overheated."

"Can we leave a message for you at your shops, or would you like a lift
home with us?" asked Roy, who felt a kind of pity for the angry and
stranded man.

"You can't do anything for me except leave me alone," snapped out
Mortlake; "you cubs are altogether too inquisitive. You're too nosy."

"But not to the extent of making sketches and notes, Mr. Mortlake?"
inquired Peggy sweetly--"cattily," she said it was, afterward.

Mortlake started and paled. Then, without vouchsafing a reply, he strode
off in the direction of the farm house to get the water he needed.

"Now, Mr. Bradbury," said Roy, extending a hand.

The young officer leaped nimbly into the chassis, and presently a buzzing
whir told that the faithful _Golden Butterfly_ was taking the air once
more.

"Score two for us!" thought Peggy to herself.

From a far corner of the pasture, Mortlake watched his young rivals
climbing the sky. He shook his fist at them and his heavy face darkened.

CHAPTER XI.

THE MARKED BILL.

Some two days after the events narrated in our last chapter, Lieut.
Bradbury, sitting in the library of the New York Aero Club, on West
Fifty-fourth Street, received a telegram from Eugene Mortlake. He was
considerably astonished, when on tearing it open, he read as follows:

"Must see you at once. Have positive proof that young Prescott is about to
sell out his secrets to foreign government."

"Phew!" whistled the young officer. "This is a serious charge. If it is
proved, it will bar Prescott from bidding for the United States government
contract. But I can hardly believe it. There must be some mistake.
However, it is my duty to investigate. Let's see--three o'clock. I can
get a train to Sandy Beach at four. Too bad! Too bad!"

The young officer shook his head. He had come to have a sincere regard for
Roy and his pretty sister, as well as admiration for their resourcefulness
and pluck.

When it is explained that during the time elapsing between his lucky lift
in the Prescott machine and the reception of the note, that Lieut.
Bradbury had notified Roy that he would be expected to report at the
Brooklyn Navy Yard, his feelings on learning that there was suspicion
directed against his young protege, may be imagined. Mortlake, too, had
received a notice that his machines were eligible for a test, so that
there would have seemed to be no object for his acting treache