The movements of the invaders of the stable, which now housed the "winged steeds" of the young aviators, were mysterious in the extreme. The Norwegian carried a tin can containing some sort of liquid which he was ordered to pour about the floor in the neighborhood of the aËroplanes. This done, Dan Cassell collected several scraps of litter and made quite a pile of it.

"All ready now, I guess," he said, with what was meant as an attempt at a grin. But his lips were pale, and his forced jollity was a dismal failure. As for his father, he made no attempt to conceal his agitation.

"Dan, they may be burned alive," he faltered; "better call it all off."

"Not when we've gone as far as this with it," was the rejoinder; "give me a match."

"Dan!"

"It's all right, dad. They'll wake in time."

"But if not?"

"Then they'll have to take their medicine."

With fingers that trembled as if their owner was palsied, Jim Cassell handed his son some matches. The latter took one, bent low over the pile he had collected and struck the lucifer.

A yellow sputter of flame followed, and the next instant he was holding it to the pile of litter which had been previously soaked by the contents of the Norwegian's can.

But before he could accomplish his purpose and set fire to the pile of odds and ends saturated to double inflammability by the kerosene the Norwegian had carried, there came a startling interruption.

There was a knock at the door and a girlish voice cried:

"Roy! Roy, let me in!"

"Furies!" exclaimed Dan Cassell under his breath. "It's one of those girls."

"Come on. Let's get away quick!" exclaimed his father, trembling from nervous agitation.

"Not before I set a match to this," exclaimed Dan Cassell viciously.

He touched the match to the pile and the flames leaped up.

"Now for our getaway," he cried, and the three fire-bugs ran for the window by which they had made their entrance.

In the meantime a perfect fusillade of blows had been showered on the door outside. Jimsy awoke just as the last of the three midnight intruders vanished through the window. His first instinct was a hot flush of shame over the feeling that he had betrayed his trust.

Then to his ears came the voice that had alarmed the Cassells and their tool.

"Roy! Jimsy! Are you there?"

"It's Peggy!" gasped Jimsy.

"And Jess," he added the next instant, and simultaneously there came the pounding of a stick on the door.

"This is an officer of the law. Open up at once."

Jimsy, dazed by his sleep, had not till then noticed the blazing pile of litter. Now he did so with a quick cry of horror. The stuff was blazing up fiercely. Already there was an acrid reek in the air.

"The place is on fire!" he shouted.

The next moment there came a violent assault on the door and the crazy lock parted from its rotten fastenings as a man attired in a police officer's uniform burst into the place. Behind him came two wide-eyed frightened girls. The leaping flames lit up their faces vividly.

"It's fire sure enough!" cried the police officer.

"Great Scot, what's happening?"

It was Roy who shouted the question. He was peering down from the loft where he had been sleeping. The uproar had awakened him and in a jiffy he was among them.

"Quick! the fire extinguishers!" he cried, and Jimsy, readily understanding, secured the flame-killing apparatus from the biplane and from the Red Dragon.

He and Roy, aided by the officer, fought the flames vigorously, and, luckily, were able to subdue them, though if it had not been for the as yet unexplained arrival of Peggy and Jess it is doubtful if they could have coped with the blaze. When it was all out Peggy rushed into explanations.

"Something warned me that you were in danger," she exclaimed, "and I woke up Jess and we found this officer and came down here."

"What gift of second sight have you?" demanded Roy, gazing at the smoking, blackened pile that had threatened the destruction of the inflammable premises.

"I don't know. Womanly intuition, perhaps. Oh, Roy!"

The girl burst into a half-hysterical sob and threw her arms about her brother's neck.

"You arrived in the nick of time, sis," he said, gently disengaging himself from her clasp, "a little more and—"

He did not finish the sentence. There was no need for him to.

"Begorry, the ould place 'ud hev bin a pile of cinders in an hour's time," declared the policeman.

It was Jess's turn to give an hysterical little sob.

Roy turned to Jimsy.

"Did you see anything? The place is reeking with kerosene. It was a plot to destroy the aËroplanes and perhaps ourselves."

"I—I—"

Jimsy stammered. The words seemed to choke up in his throat. How was he to confess that he had failed in his trust—had slept while danger threatened?

"Well?"

Roy waited, plainly surprised. It was not like Jimsy to hesitate and stammer in this way.

At last it came out with a rush.

"I—I—you'll never forgive me, any of you—I was asleep."

"Asleep! Oh, Jimsy!"

There was a world of reproach in Jess's voice. But Peggy interrupted her.

"How was it, Jimsy?" she asked softly.

"I don't know. I give you my word I don't know."

Jimsy's voice held a world of self-reproach.

"I was reading," he went on, hurrying over the words as if anxious to get his confession over with, "that book of Grotz's on monoplane navigation. I felt sleepy and—and the next thing I knew I woke up to hear you pounding on the door and shouting."

"A good thing the young ladies found me," put in the policeman; "shure I was after laughing at them at first, but then, begorry, I decided to come along with them. It's glad I am that I did."

"Who can have done this?" asked Roy, who had not a word of reproach for his chum, although Jimsy had failed dismally in a position of trust.

"Begorry, they might have burned you alive!" cried the policeman indignantly.

"No question about that," rejoined Roy; "it was a diabolical plot. Who could have attempted such a thing?"

"Wait till I call up and have detectives sent down here," said Officer McCarthy. "I'm after thinking this is too deep for us to solve."

Nevertheless, each of that little group but the policeman had his or her own idea on the matter.