quiet, or——"

"Roy Prescott," enunciated Peggy, severely shaking one pink-tipped finger under Roy's freckled nose, "this is not a subject for jesting."

"Never more serious in my life, Sis. If you could have seen your own face as you peeked through those glasses——"

Peggy stuffed the binoculars into her brother's brown hands.

"Here, look for yourself," she ordered. Her voice was so imperious that Roy obeyed immediately.

An instant later his sister's expression of dumfounded amazement was mirrored on his own straightforward, good-looking countenance.

"Well, as Bud used to say out West, 'if that ain't the beatingest'!" he gasped.

"What did you read?" demanded Peggy breathlessly. "Repeat it so that I may be sure my eyes didn't play me a trick."

"Not likely, Sis; the letters are big enough. They show up on that red painted barn of a place like a big freckle on a pretty girl's chin."

Then he repeated slowly, mimicking a boy reciting a lesson:

"The Mortlake Aeroplane Company. Well, wouldn't that jar you?"

"Roy!" reproved Peggy.

"There's no other way to express it, Sis," protested the boy. "Why, that's the concern that's been advertising so much recently. Just to think, it was right at our door, and we never knew it."

"And that hateful old Mr. Harding is interested in it, too, oh!"

The exclamation and its intonation expressed Peggy's dislike of the gentleman mentioned.

"It's a scheme oh his part to make trouble for us, I'll bet on it," burst out Roy. "But this time I guess it's no phantom airship, but the real thing. What time is that naval lieutenant coming to look over the Prescott aeroplane, Peggy?"

"Some time to-day. He mentioned no particular hour."

"Do you think it possible that he is also going to take in that outfit down the road?"

"It wouldn't surprise me. Maybe that's why they are just putting up the sign. They evidently have refrained from doing so till now in order to keep the nature of their business secret. If we hadn't come back from Nevada sooner than we expected, we might not have known anything about it till the navy had investigated and—approved."

Far down the road, beyond the big red building, came a whirl of dust. From it presently emerged a big maroon car. Peggy scrutinized it through the glasses.

"Mr. Harding is in that auto," she said, rather quietly for Peggy, as the car came to a stop in front of the Mortlake Aeroplane Manufacturing Company's plant.

Shortly before Peggy and Roy Prescott, their aunt, Miss Sallie Prescott, with whom they made their home, and their chums, Jess and Jimsy Bancroft, had returned from the Nevada alkali wastes, the red building which engaged their attention that morning had caused a good deal of speculation in the humdrum Long Island village of Sandy Beach. In the first place, coincident with the completion of the building, a new element had been introduced into the little community by the arrival of several keen-eyed, close-mouthed men, who boarded at the local hotel and were understood to be employees at the new building. But what the nature of their employment was to be, even the keenest of the village "cross examiners" had failed to elicit.

Before long, within the freshly painted wooden walls, still sticky with pigment, there could be heard, all day, and sometimes far into the night, the buzz and whir of machinery and other more mystic sounds. The village was on tenter-hooks of curiosity, but there being no side windows to peer through, and a watchman of ferocious aspect stationed at the door, their inquisitiveness was, perforce, unsatisfied. Not even a sign appeared on the building to indicate the nature of the industry carried on within, and its employees continued to observe the stoniest of silences. They herded together, ignoring all attempts to draw them into conversation. What Peggy and Roy had observed that day had been the first outward sign of the inward business.

From the throbbing automobile, which the boy and girl had observed draw up in front of the Mortlake plant, a man of advanced age alighted, whose yellow skin was stretched tightly, like a drumhead, over his bony face. From the new building, at the same time, there emerged a short, stout personage, garbed in overalls. But the fine quality of his linen, and a diamond pin, which nestled in the silken folds of his capacious necktie, showed as clearly as did his self-assertive manner, that the newcomer was by no means an ordinary workman.

His face was pouchy and heavy, although the whole appearance of the man was by no means ill-looking. His cheeks and chin were clean shaven, the close-cut beard showing bluely under the coarse skin. For the rest, his hair was black and thick, slightly streaked with gray, and heavy eyebrows as dark in hue as his hair, overhung a pair of shrewd, gray eyes like small pent-houses. The man was Eugene Mortlake, the brains of the Mortlake Company. The individual who had just descended from the automobile, throwing a word to the chauffeur over his shoulder, was a person we have met before—Mr. Harding, the banker and local magnate of Sandy Beach, whose money it was that had financed the new aeroplane concern.

CHAPTER II.

MR. HARDING DECLARES HIMSELF.

Readers of the first volume of this series, "The Girl Aviators and The Phantom Airship," will recall Mr. Harding. They will also be likely to recollect his son, Fanning, who made so much trouble for Peggy Prescott and her brother, culminating in a daring attempt to "bluff" them out of entering a competition for a big aerial prize by constructing a phantom aeroplane. Fanning's part in the mystery of the stolen jewels of Mrs. Bancroft, the mother of Jess and Jimsy, will likewise be probably held in memory by those who perused that volume. The elder Harding's part in the attempt to coerce the young Prescotts into parting with their aerial secrets, consisted in trying to foreclose a mortgage he held on the Prescott home, with the alternative of Roy turning over to him the blue prints and descriptions of his devices left the lad by his dead father. How the elder Harding was routed and how the Girl Aviator, Peggy Prescott, came into her own, was all told in this volume. Since that time Mr. Harding's revengeful nature had brooded over what he chose to fancy were his wrongs. What the fruit of his moody and mean meditations was to be, the Mortlake plant, which he had financed, was, in part, the answer.

In the volume referred to, it was also related how Peter Bell, an old hermit, had been discovered by means of the Prescott aeroplane, and restored to his brother, a wealthy mining magnate.

In the second volume of the Girl Aviators, we saw what came of the meeting between James Bell, the westerner, and the young flying folk. By the agency of the aeroplane, a mine—otherwise inaccessible—had been opened up by Mr. Bell in a remote part of the desert hills of Nevada. The aeroplane and Peggy Prescott played an important part in their adventures and perils. Notably so, when in a neck-to-neck dash with an express train, the aeroplane won out in a race to file the location papers of the mine at Monument Rocks. The rescue of a desert wanderer from a terrible death on the alkali, and the routing of a gang of rascally outlaws were also set forth in full in that book, which was called "The Girl Aviators on Golden Wings."

The present story commences soon after the return of the party from the Far West, when they were much surprised—as has been said—to observe the mushroom-like rise of the Mortlake factory. But of what the new plant was to mean to them, and how intimately they were to be brought in contact with it, none of them guessed.

"Well, Mortlake," observed Mr. Harding, in his harsh, squeaky voice—not unlike the complaint of a long unused door, "well, Mortlake, we are getting ahead, I see."

The two men had, by this time, passed within the