O’Brien burst out with an exclamation of anger, “By gosh, sir, this thing is going too far! I don’t intend to stand by and see you murdered. You have had a close shave here tonight, and something has got to be done. Where is Mrs. Ridgeway?”

“She is in England visiting some relatives,” said Mr. Ridgeway with a triumphant laugh. “So you won’t get any backing from her. I sent her over there three months ago.”

“Well, something has got to be done all right, all right,” said the secret service man sullenly.

Mr. Ridgeway pressed his aching head. “I think this will end it,” he said. “They have found no papers, and they will let well enough alone. You know as well as I do, O’Brien, that they will know that I will be on guard after this. And I will be. I will set a lot of detectives around here, each with a badge as big as a dinner plate. And I will sit and do nothing, and you can do the work.”

“All right; that is more like what I want to hear,” said O’Brien, smiling at last. “You are doing enough, Mr. Ridgeway, when you finance the affair. You have had all those airplanes built, and those dirigibles, and if you sit tight and boss, that is all we will ask for. Just you let me and Lawrence push the rest of the work.”

“I will have to keep quiet for a day or two anyway,” said Mr. Ridgeway. “I feel sort of old tonight. I wish I had a son or two to look out for me. But you are all right, O’Brien. Do whatever you like.”

“Then to bed you go, first of all,” said the practical Irishman, “and whilst I get some plainclothes men here for a guard, you can sit with him, Lawrence, and don’t you let a soul in the room.”

“The servants are all in bed and there is no one else to come,” said Mr. Ridgeway drowsily.

With a good deal of help he managed to get to the little automatic elevator, and they put him to bed. While Lawrence put cold compresses on the bruised head, O’Brien telephoned for the police and placed a guard around the house. Then he summoned Mr. Ridgeway’s doctor, who examined the wound and assured them that there was no concussion. By the time all this was done, it was nearly three o’clock in the morning.

“Let’s to bed,” yawned O’Brien. “It’s coming home with you I am, Larry. I expect you’ll loan me the matter of some pajammies?”

“Sure!” said Lawrence. “But I don’t know how they will fit.”

“Fit, fit!” said O’Brien, hailing a passing taxi. “Fit? Sure, I could sleep this night in lead pajammies, any size whatever.”

True enough, O’Brien rolled into bed and was asleep in a moment, but Lawrence tossed restlessly a long time before he could quiet himself. He was worried about Mr. Ridgeway, and he wished O’Brien would wake up and tell him just what he feared from the spies or conspirators, or whatever they were. And he wondered about Mr. Ridgeway, and was sorry that he had no sons, and wished, poor Lawrence, that he was Mr. Ridgeway’s son. How proud he would be! But he knew that he would always be Lawrence Petit, the waif, with only a pictured face for a family.

O’Brien snored on gently and endlessly, and at last, lulled by the sound, Lawrence went to sleep. When he awoke, O’Brien was in the bathroom running a bath, and singing Sweet Rosy O’More in a mellow baritone. He sounded like a man who has not a care in the world.

Lawrence jumped up. It was eight o’clock. They had overslept an hour. But when he asked O’Brien how he had happened to sleep so late, that songful gentleman declared that there was nothing to do but enjoy themselves and he intended to go to a movie and sit through it twice, so he could think.

“Will you go along with me?” he asked.

“I would rather fly,” said Lawrence. “I wish I could get hold of a plane. I would feel better if I could get off the earth for a while. I can never think so well as when I am up a few hundred feet.”

“Go as high as you like,” said O’Brien. “Here, I will give you a bit of a paper, and just you go out to the field and give it to the man in charge there, and all that you will have to do after that is to pick which plane you want. You can’t use the dirigible because it is smashed up.”

“I would rather have a plane to-day,” said Lawrence. “I want to get used to the country around here. I shall drive the dirigible when it is in order, but I like to take my bearings first. It is funny, I have flown all over the United States and Europe, but this is the first time I was ever in Washington.”

“Well, take one of the little sky-flivvers and have a good time, but be careful about landin’. A nose-dive or a tail-spin makes good readin’ in the Sunday papers, and you get a grand write-up all about the darin’ young aviator So-and-So, but it’s little interest you feel in the article yourself.”

Lawrence took a street car out as far as he could, and after a brisk walk reached the field. Everything was going smoothly. He offered his paper to the man in charge, and that individual, after grumbling a little at letting a kid go up with a perfectly good machine, let Lawrence look the twenty planes over and choose the one he fancied.

Lawrence refused a passenger, and with a good start soared off the field and rose until the city of Washington lay far below him. He had not made a flight for a couple of weeks, and his heart thrilled. After a few wide circles that took in the shipping at the Navy Yard and all the outlying parts of the city, he flew over Baltimore. The return he made low, and studied the woods and landing places, to make himself sure of his ground.

As he neared Washington again, he saw a plane approaching from the south. It came straight for him, and he had an idea that it was trying to communicate with him by means of the wireless. He glanced down and found that, contrary to usage, his own machine was not equipped. So he paid no attention to the stranger other than to swerve out of the way. But the plane turned and followed. Lawrence, curious to know what it was up to, slowed down and allowed it to overtake him. His trained ear told him by the sound of the engine that his own plane was the faster and more powerful but he had no intention of racing as he thought the other pilot wanted to do.

So he slowed down, and as the other machine came alongside he saw that they were flashing messages with a mirror, using the Morse code, which had become one of the requirements in the public schools.

“Who are you?” demanded the stranger. “Who are you?” over and over. Lawrence had no mirror and for a moment was at a loss how to reply. There was something threatening about the manner of the other plane, and Lawrence had no desire to get into a combat in the clouds over nothing. He had an idea, and as the other plane imperiously repeated the words he managed to take off the muffler, and in the roar of the engine he spelled out:

“A tourist seeing the sights. Who are you?”

“Where from?” demanded the mirror.

“Louisville. Who are you?” repeated Lawrence.

The plane evidently had the answer they wanted and, sheering off, shot away without a reply. Lawrence set his teeth. If they could be so discourteous he could follow at all events, and see where the curious plane hailed from. He wheeled his machine and, taking a higher level, sailed off in pursuit, keeping a good distance behind. An hour’s flight brought them above a small open field and here the plane suddenly dipped, and going at a breakneck angle dropped to the ground. Then as though by magic it disappeared. There was no hangar, yet the machine went under cover as though the earth had swallowed it.

Again and again Lawrence circled the field, and it worried him to imagine the chuckles the other pilot was indulging in at his expense.

Try as he might, he could not locate any sign of life. It struck him as a rather queer thing. He turned his nose upward again, and located the field by some trees and other landmarks, then turned toward the home field.

Dropping easily down, he found O’Brien surrounded by a group of men, all of whom seemed to be watching him with a good deal of interest.

“Hey, young felly,” called O’Brien, “do you always make so neat a landing as that last?”

“I suppose so,” answered Lawrence. “What was there about that one?”

“It was all right; that was it,” said O’Brien. “If that’s the way you fly, you can have all me pretty toys at once, on a string.”

“One is enough,” laughed Lawrence. “Don’t you want to go up?”

“I wouldn’t mind a short flight, just to see how you manage it,” said O’Brien, gently relieving the man next him of his helmet and goggles.

Rising once more, Lawrence waited until they had gained a good height, then as they sailed along in a steady current, he told O’Brien of his encounter and the curious thing about the landing place of the strange car and its sudden disappearance.

“Let’s go over there,” said O’Brien. “It’s just the sort of thing I have to look after. What with the country full of Reds, and all other colors of the rainbow, we want to keep as many of the wild lunatics under observation as possible.”

They soon reached the spot where Lawrence had seen the plane land and, sure enough, there was not a sign of anything that could be taken for a hangar.

“You sure this is the place?” asked O’Brien.

“Sure!” replied Lawrence. “What do you say to landing? I can make it easier than he did.”

“Land away if ye like, and let’s have a look,” said O’Brien, “but don’t you smear me all over that nice green grass, I warn you.”

“I won’t,” promised Lawrence, and dropped to earth as lightly as a bird.

As the plane slid along the grass and came to a standstill, O’Brien gave a smothered exclamation.

“That’s funny!” he said. “Look!”

Stepping out of the machine, Lawrence turned in the direction O’Brien was looking. The hangar they were looking for was there, but covered with a thick-set camouflage of brush. The doors were open, as though no one would possibly find the place, and inside the hangar were three cars: one a dirigible, one the car Lawrence had encountered, while the third was a long, rakish model mounting an aircraft gun.

One quick look, and O’Brien backed out, drawing Lawrence with him. He motioned him into their own plane, gave it a push and hopped into his place as the speedy little flyer danced along for a moment, then rose into the air.

As they fled, O’Brien mopped his brow.

“I didn’t feel that place to be so healthy for us,” he said. “And a gun looking so fit! Who said the war was over these five years? Now what in the world of wonders does all that mean? I dunno. Do you?”

Lawrence shook his head.

“Don’t go there again,” warned O’Brien. “Whether I’m with you or no. Do you mind? We have got to find out about it. Did you notice anything funny about that dirigible? No? Well, you don’t know as well as I do, but that old tube is exactly like the one that got cut up last night. Down to the last seam, and even a dent in the steerin’ gear that I made meself trippin’ against it with a hammer in me hand.”

“How do you suppose that happens?” asked Lawrence, his eyes fixed in the distance.

“That’s what I dunno,” said O’Brien. “But the joke is that I don’t think it happens at all. There is something funny about that. Dang funny!”

“Where do you suppose the people were?” asked Lawrence.

“Off amusin’ themselves, or up to some mischief,” answered O’Brien. “They have such a good hidin’ place that they don’t bother to guard their cars at all, at all.”

They landed, O’Brien still sputtering. But Lawrence was silent. He quizzed O’Brien about the locality and learned that it was not far from the railroad. Then finding that O’Brien had an engagement for the evening, he went quietly away. He first went to his rooms, took some money from the trunk, and put on a dark suit. Then he hurried down town, and reaching the Union station, boarded a train and was soon out of the city. He had dinner on the train, and at about nine o’clock reached the little station of Linden, where he dropped off and not waiting for the train to pull out, slipped across the track and was swallowed up by the shadows.

For all his athletics, Lawrence hated walking, as most aviators do, and he groaned in spirit as he trudged over the country in what he hoped was the direction of the mysterious aviation field. It had not occurred to him to ask anyone how to reach it. Instinctively he knew that the mysterious cars had not been heralded to the country at large.

He lost time, and several times had to turn aside and almost retrace his steps, but at last he knew from the lay of the country that he was in the right neighborhood. The moon had risen and was full. It cast the densest shadows and Lawrence slipped from one patch of blackness to another. He felt silly. He was not sure that this was not a wild goose chase. The cars might be the property of some eccentric man who wished to keep them in seclusion, and possibly he was trespassing on private ground. He plodded on, however, urged by an impulse he could not understand.

At last he emerged suddenly on the very aviation field itself; and on the other side he saw the big bulk that was the hangar. Once more plunging into the underbrush, he skirted the field and circled it until he found himself at the back of the hangar. There was a small door here, half open, and from within he heard voices.

He could not hear what was being said, however, and he took the chance an older man would have thought plain suicide. Entering the door, and fairly holding his breath, he stepped slowly and carefully along the side of the building, crept close to the little plane, and finally lay down and wriggled beneath it toward the dirigible. On the other side of the long body four men were sitting over a game of cards. Not until Lawrence felt the cool box of the plane above him did he think of danger. And then it came to him clear as the tolling of a bell ... discovery meant his death!