It was perhaps four hours later, or a little after midnight, when all four of the young men were suddenly and simultaneously aroused from their peaceful slumbers by the loud clanging of a gong.

No need to ask what it was, even when coming out of a deep sleep. It was a fire bell, and pealing out in quick, insistent warning calls!

"Great guns!" shouted Fred Bentner, the first out of his bunk and to a window. "There's a fire all right, and it's over at the hangars."

The wild scrimmage which followed was probably repeated in every one of the half dozen near-by huts in which the respective crews were quartered.

Big Jack Carew went crashing out the door, still drawing his shirt over his head and wearing only one shoe. Don, in his own excitement, had kicked the other under a cot, and Carew had refused to take time to look for it. He was followed by Andy Flures, who certainly was not attired for a parlor reception; and the other two were only a few steps behind.

"I believe it's our own hangar," breathed Big Jack, his tones reflecting an agony of suspicion and suspense.

At that instant Bentner, who hadn't stopped for any shoes at all, stubbed his toe on a protruding rock.

"Holy cats!" he ejaculated, grabbing the injured foot and hopping along in terrible pain. "Oh, my golly, my toe!"

"Stick it in your pocket and come along," advised Andy, as he sped by.

Men were turning out of every hut in all sorts of garb, none of them fully clothed, some of them still in pajamas and whatever they could find first in the way of footwear. Meanwhile the great gong continued its clamor, there was the more strident banging of engine bells, and the townspeople came streaming forth, too, to add to the excitement.

And during this brief time little tongues of flame were leaping upward, apparently from the rear of the hangar in which was stored the great dual-motor plane in which our four friends hoped to be the first across the Atlantic.

The firemen were just getting a stream on the blaze when the youths arrived.

"Well, thank our lucky stars for that," exclaimed Don Harlan as he realized that, devilish as the evident plot had been, it had not succeeded to the point of setting fire to their hangar.

The blaze was in a large box of excelsior, which had been placed close to the rear boarding of the hangar. There was no doubt but that someone had set about deliberately to destroy that structure and the machine within. That the plan had not succeeded, it turned out later, was due to the fact that a private watchman, smelling smoke and tracing it to its source, had discovered the flames before they had entirely consumed the excelsior. He had pulled the big box a few feet away from the building and then had sounded the alarm.

The mystery lay in who wanted to destroy that hangar, and how he had dragged the box there without being discovered.

Extinguishing the fire was, of course, but a matter of a few moments. Immediate examination was made of the box. Unfortunately it had been partly consumed and the fire had, as fate would have it, eaten away that particular part which undoubtedly would have revealed to whom originally it was consigned.

There was no question in the minds of anyone, however, but that it was one of the sort in which practically every crew that was to participate in the flight had received a part of its equipment.

"There's something rotten in Denmark, all right, to quote our friend Shakespeare again," said Big Jack Carew, "and it's plain enough that we've got to use every precaution against accident from now on. Somebody is trying to put us out of this contest. We might thank them for the compliment, but I wish they would just come out into the open sufficiently to reveal their identity."

"Well, there isn't any doubt in my mind that we frustrated the original plot ourselves," added Fred Bentner, who by this time had hobbled up, and had taken in the whole situation from the little he had seen and the snatch of conversation he had heard.

"Yes," agreed the other two. "No doubt about it now. The fellow we saw sneaking around here earlier in the night was bent upon mischief."

"And if I get my hands on him I'll have him in the calaboose before he knows what's happened to him," added a voice from behind, and all four turned to confront Captain Isaac Allerson, late sailor of the northern seas, onetime whaling captain, and now, by virtue of the votes and confidence of his fellow-citizens, the town "constabule."

He looked at them significantly and there was something threatening in his attitude. They were not slow to remember where and under what circumstances they had heard practically those identical words before.

"Do you think—" Big Jack Carew began, and then stopped.

"Young man," the ex-whaler supplemented, "I'm thinkin' a whole lot of things I ain't sayin' just now. But you can bet yer last dollar that I'm keepin' both eyes peeled and both ears open."

Instinctively they gazed over the throng that still stood about, even though the fire was now entirely extinguished.

"Huh!" Captain Allerson exclaimed, and suddenly walked away.

In a moment he approached the unpopular, and at that moment unsuspecting, Henryson, who was standing on the outer edge of the crowd.

"That's strange," was the old seaman's expression, in a tone loud enough for all to hear, and attracting instant attention.

"What is?" asked Henryson, who could not ignore the fact that it was he who was being addressed. Bentner asked the others later if they, too, thought that a half-frightened look came into the Norwegian's eyes as the mentor of law and order addressed him.

"Why," Captain Allerson replied, slowly, and in bitingly incisive tones, "you seem to be about the only one around here that had time to stop and dress fer this here surprise party tonight."

Henryson muttered something about having been cold, and sleeping with his clothes on, and then abruptly turned and stalked away toward the hut he was occupying.

"Bad egg, that," growled the old sea captain, as he came over again to Big Jack and the members of his crew.

But he had time for no more, for the members of the other crews had gathered around to congratulate the youths on the fact that the fire had been discovered in time, and to speculate as to who the villain was who had tried to burn them out.

True sportsmen that they were, the young men said nothing of their suspicions, and the others, if they shared such thoughts, kept them to themselves.

There was instant agreement, however, that with a skulking incendiary around, no hangar or its valuable contents was safe, and that the best insurance against a hidden foe lay in a constant night patrol by at least two men. It was arranged, therefore, that two would continue such watchfulness throughout that night, and that thereafter, until the flight began, this vigilance would be kept up by two men on duty throughout the entire time from sunset to sunrise, each couple doing duty for four hours.

In the drawing of lots which followed, Don Harlan and a man named Joe Harrity were selected to patrol the hangar section throughout the balance of that night; and this was completely satisfactory to all concerned, for they were equally popular and trusted among their fellow aviators.

Naturally, with the entire town so aroused, not even the boldest malefactor would be expected to pay another pilgrimage to the scene of his attempted work of arson that same night, and nothing further happened, although both Don and Harrity held secret hopes that the fellow would put in an appearance, so that they might at the same time learn his identity and his motive.

Early in the morning Jack, Fred and Andy had a hasty breakfast and then hurried to the hangar just as Don was returning to snatch a few hours' sleep to make up for the long vigil.

"See anything further?" Jack asked.

"No," Don answered. "The fellow, whoever he is, didn't return, but I wish he had."

"Well, we're going over every inch of that plane today," Jack informed him. "But I've just been thinking that it might be best not to say anything; in fact, to make it seem that our suspicions have been lulled to sleep."

"Yes," said Don, "I'm inclined to believe, with you, that that is our best method of self-protection."

"All right, then, we'll say nothing to anybody. If we discover anything it may help us to solve this mystery."

Don continued to the hut, where he warmed up the breakfast the other three had left for him. Meanwhile they were at the hangar, beginning their minute examination of their plane.

It was well toward noon, and when they were coming to the conclusion that no matter what might have been the designs against them, none had been successfully carried out, when Andy made a sudden exclamation which brought the others to his side.

For more than an hour he and Jack had gone over the engine together, while Fred had made every possible test of the electrical and radio equipment. Jack and Fred were at this time examining the elevators and rudder, and Andy was going over the fusilage, carefully inspecting every inch of strut and frame work, and by accident had laid his hand on one of the main bracing wires. His trained touch had brought the involuntary exclamation.

"What is it?" Jack asked, as nearly excited as he ever permitted himself to get.

For a moment Andy did not reply. When he did it was to ask the others to come closer.

"Look at this," he said, pointing with index finger to a place far up on the bracing wire.

Now it may be explained here that for the purposes of strength and endurance these wires are made up of many smaller strands, finely twisted together. Sometimes one of these strands will break, and often a careless aviator, or an over-confident one, or one who does not want to subject himself to what he regards as an unnecessary delay, although he knows the danger inherent in such a course, will clip off the broken strand, close up to the main wire of which it is a part, and do the job so well that even a trained inspector might not easily discover how, to save time, he was endangering his own safety and perhaps the lives of others.

During the war, when often time was the main objective, when danger was laughed at, and even human life was valued cheaply, many an aviator came to his death through a collapse of his machine directly due to the fact that he or other aviators, perhaps over a considerable period, had clipped off and thus hidden so many broken strands in a single wire that finally it broke completely, perhaps telescoping the entire machine.

In this instance Andy had discovered at least half a dozen broken and carefully hidden strands of a single important bracing wire, and there was no doubt that it had been done deliberately by someone planning the ruin of that plane long after it was on its way from America to Europe.

For a moment the very dastardliness of the deed was so disconcerting that the three youths found themselves speechless. There was no doubt of the meaning of the discovery. The plot was a daring one to defeat this machine and crew in the race, and it had been designed and carried into effect in a way that, had it not been discovered in time, probably would have cost them their lives.

"Well," ejaculated Jack, the first to recover himself. "Somebody certainly loves us."

"Yes," said Andy, "they wish us well—well out of the way."

From the window they could see Donald approaching, refreshed by his morning's nap.

"Let's wait until he gets here," Fred suggested, "and then hold a council of war."

In a few words Donald was told of the situation. At first they thought it would be well to take Captain Allerson into their confidence, but on calmer consideration they agreed that he might inadvertently drop the tip, and then, after all, the culprit might not be caught, with the resulting danger that this or some other machine would start upon the flight mortally crippled, destined never to reach Europe.

"Better keep the thing to ourselves for a day or two, anyway," was Jack's counsel, "and then determine how we are to let the others know."

"Well, I'll tell you what I'm going to do," said Fred Bentner, his countenance set determinedly and a glint in his fine eyes. "I'm just going to fix this machine so that anyone who touches it will stay here until we arrive."

"How?" asked Andy Flures.

"I'm going to charge every metallic part with a sufficient voltage of good old electric juice to give the shock of his life to anyone who lays his hands upon those parts," Fred answered.

"That's the best idea yet," agreed Jack enthusiastically. "That is, providing you can give it sufficient voltage."

"Well," Fred went on, "I'll connect up enough of the juice that even if it won't hold a man it'll bring such a surprised yell out of him that anybody within a hundred yards will know he has touched something hot."