It was the next evening. Mortlake, sitting at his desk, looked up as a quick step sounded outside. The factory was in darkness as the men had gone home. Only a twilight dimness illuminated the little glass sanctum of the inventor and constructor of the Mortlake Aeroplane.

"Come in," said Mortlake, as the next instant a sharp, decisive knock sounded.

Lieut. Bradbury, in a mufti suit of gray, stepped into the office.

"Ah, good evening, lieutenant," said Mortlake, rising clumsily to his feet and offering a chair, "I was beginning to despair of you."

Bradbury, genuinely worried, lost no time in plunging into the object of the interview.

"That message you sent me—what does it mean?" he asked. "I can scarcely believe——"

"Nor could I, at first," said Mortlake, with assumed sorrow. "It cut me pretty deep, I tell you, to think that a boy who was in negotiations with his own government for a valuable implement of warfare, should deal with a foreign government at the same time. In brief, this young traitor is balancing the profits and will sell out to the highest bidder."

"That's strong language, Mortlake," said the young officer, drumming the table with his fingers impatiently. Honorable and upright in all his dealings, the young officer had no liking for the business in hand. Yet it was his duty to see the thing through now, unpleasant as it promised to be.

"Strong language?" echoed Mortlake. "Yes, it is strong language, but not a bit more emphatic than the case warrants. Did you know that for some days past a German spy has been in Sandy Beach?"

"No. Certainly not."

"Well, there has been. He visited this plant with proposals to turn over our aeronautic secrets to his government, but we refused to have anything to do with his scheming."

"Yes, very good. Go on, please." The young officer felt that Mortlake was approaching the climax of his story.

"One of our men," resumed Mortlake, in even tones, in which he cunningly managed to mingle a note of regret, "one of our men took upon himself—loyal fellow—to watch this spy. He reported to me some days ago that the man was in negotiation with young Prescott."

"Good heavens!"

"I know it sounds incredible, but we are dealing with facts. Well, more than this, my zealous workman ascertained that young Prescott is to meet this foreign agent at nine o'clock to-night on a lonely road, and is there to hand over to him the complete plans and specifications of the Prescott aeroplane."

"It's unbelievable, horrible. And in the face of this, do you mean to say that the boy would dare to keep up his apparent negotiations with the United States?"

"That's just the worst part of it, as I understand it," rejoined Mortlake. "The negotiations with this foreigner would, of course, be presumed by young Prescott to be secret. This being so, he would, if successful in the tests, sell his ideas to the United States also, without mentioning the fact that they had already been bought and paid for."

"Monstrous!"

"Just what I said when I heard of it. I could not believe it, in fact. The boy has always seemed to be all that was upright and honest. It just shows how we can be mistaken in a person."

"I cannot credit it yet, Mortlake."

"It was to give you proof positive that I summoned you here. We will take an automobile out to the spot where young Prescott is to meet the foreign agent. Of course, our arrival will be so calculated as to give us time to secrete ourselves before Prescott and the other meet. Are you willing to let your estimate of young Prescott stand or fall by this meeting?"

"I am, yes," replied Lieut. Bradbury, breathing heavily. "The young scoundrel, if he is caught red-handed, I will see if there is not some law that will operate to take care of his case."

Mortlake could hardly conceal a smile. His plan to ruin Roy was working to perfection. In his imagination he saw the Prescott aeroplane eliminated as a naval possibility, and the field clear for the selection of the Mortlake machine. Mentally he was already adding up the millions of profit that would accrue to him.

Lieut. Bradbury left that meeting heavy of heart. Mortlake's story had been so circumstantial, so full of detail, that it hardly left room for doubt. And then, too, he had offered to produce positive proof, to allow the officer to witness the actual transaction.

"Good heavens, isn't there any good in the world?" thought the officer, as the hack in which he had driven out to the Mortlake plant drove him back to the village. Mortlake had agreed to call for him at the little hotel at eight o'clock. The hours till then seemed to have leaden feet to the anxious young officer.

It was shortly before this that Roy, returning from an errand in town in the Prescott automobile, was halted at the roadside by a figure which stepped from the hedge-row, and, holding up a cautioning finger, uttered a sharp:

"Hist!"

Roy, turning, saw a man, seemingly a workingman, from his overalls, at the side of the machine.

"What is it? What do you want?" demanded Roy.

"I have a message for you," said the man, speaking in a slightly foreign accent; "you are in great danger. Your enemies plot it."

"My enemies!" exclaimed Roy.

"Yes, your enemies at the Mortlake factory."

"Let's see," said Roy thoughtfully, "you're one of the workmen at the Mortlake plant, aren't you?"

"I was once," said the man, with a vindictive inflection, "but I am so no longer. Mortlake discharged me."

"Discharged you, eh? Well, what's that got to do with me?"

Roy looked curiously at the man.

"Just this much. I know the meanness that Mortlake plans to do to you. You have bad and wicked enemies at our place."

"Humph! I guess there may be some truth in that," said Roy with a rather grim inflection. "Well, what do you want me to do about it?"

"Just this: I am an honest man. I do not want to see harm come to you or to your sister." This was touching Roy in a tender spot.

"To my sister!" he exclaimed. "Do you mean to say that Mortlake is scoundrel enough to plot against her, too?"

"In this way," explained the man, "he means to destroy your aeroplane, leaving the field clear for his own type to be selected by the navy."

"The—the—the ruffian!" panted Roy, now thoroughly aroused. "Tell me more about this."

"I cannot," rejoined the workman, "but my partner—he was discharged too—he can tell you much, much more. Will you meet him? I can take you to him?"

Roy thought a moment. The man seemed to be wholly honest and in earnest.

"How far from here is the place where your partner is?" he asked.

"Oh, not so very far. We soon get there in your fine machine. Will you go?"

"Well, I—yes, I'll go. Come on, get in."

The man obeyed the invitation with alacrity. Under his directions, Roy swung the car off upon a by-road after they had gone some few hundred yards.

"Not long now," he said, as the vehicle bounced and jounced over the ruts and stones of the little-used thoroughfare.

"This is a funny direction for your partner to live in," said Roy at length. "There are not many dwellings out this way, nothing but a big swamp, as I recollect it."

"My partner, he poor man," was the rejoinder. "He live with cousins out here."

The answer lulled Roy's rousing suspicions.

"It must be all right," he thought. "There can't be any trick in all this. It's quite likely that Mortlake does want to play us a mean trick. I can't forget the look he flashed at me the day we took Lieut. Bradbury away from him in that meadow after we had made our first sea trip. Wow!"

Roy could not forbear smiling at the recollection.

They chugged along in silence for some little distance farther, and then the man beside him laid a detaining hand on Roy's arm.

"Almost there now," he said. "Better slow up."

Roy did so. The brakes ground down with a jarring rasp.

At the same moment a dark figure stepped from behind a tree trunk. The man beside Roy held up a hand.

"This is the young gentleman," he said.

Through the gloom the other figure now approached the automobile.

"Do you mind getting out?" it said. "We can talk better in the house."

"Where is the house? I don't see one," said Roy, his suspicions rousing a little.

"It's just behind that knoll. The path is just ahead," said the newcomer.

Roy got out. He was determined to see the adventure through now. If Mortlake was plotting against him, he wanted to know it.

As he reached the ground, the newcomer extended his hand, as if offering to shake Roy's palm.

Roy put out his hand, which was instantly grasped by the other.

"Your friend tells me that you have something interesting to tell me——" began Roy. "I—here, what are you trying to do? Stop it!"

The other had seized his hand in a clutch of steel, and, before the astonished boy could offer any resistance, had wrenched it over in such a manner that, without exactly knowing what had occurred, Roy found himself sprawling on his back.

The lad was helpless in this lonely place with two men who had now shown themselves in their true and sinister character.