"I hope he'll be all right," said Dick.

"They'll find him, I'm sure," said Harry. "Even if they don't, he'll be all right for a few days—two or three, anyhow. A man can be very uncomfortable and miserable, and still not be in any danger. We don't need half as much food as we eat, really. I've heard that lots of times."

They were riding along the line that Harry had marked on his map, and, a mile or two ahead, there was visible an old-fashioned house, with a tower projecting from its centre. From this, Harry had decided, they should be able to get the view they required and so locate the second heliographing station.

"How far away do you think it ought to be, Harry?" asked Dick.

"It's very hard to tell, Dick. A first-class heliograph is visible for a very long way, if the conditions are right. That is, if the sun is out and the ground is level. In South Africa, for instance, or in Egypt, it would work for nearly a hundred miles, or maybe even more. But here I should think eight or ten miles would be the limit. And it's cloudy so often that it must be very uncertain."

"Why don't they use flags, then?"

"The way we do in the scouts? Well, I guess that's because the heliograph is so much more secret. You see, with the heliograph the flashes are centered. You've got to be almost on a direct line with them, or not more than fifty yards off the centre line, to see them at all, even a mile away. But anyone can see flags, and read messages, unless they're in code. And if these people are German spies, the code wouldn't help them. Having it discovered that they were sending messages at all would spoil their plans."

"I see. Of course, though—that's just what you said. It was really just by accident that we saw them flashing."

Then they came to the house where they expected to make their observation. It was occupied by an old gentleman, who came out to see what was wanted and stood behind the servant who opened the door. At the sight of their uniforms he drew himself up very straight, and saluted. But, formal as he was, there was a smile in his eyes.

"Well, boys," he said, "what can I do for you? On His Majesty's service, I suppose?"

"Yes, sir," said Dick. "We'd like to go up in your tower room, if you don't mind."

"Scouting, eh?" said the old gentleman, mystified. "Do you expect to locate the enemy's cavalry from my tower room? Well, well—up with you! You can do no harm."

Dick was inclined to resent the old gentleman's failure to take them seriously, but Harry silenced his protest. As they went up the stairs he whispered: "It's better for him to think that. We don't want anyone to know what we're doing, you know—not yet."

So they reached the tower room, and, just as Harry had anticipated, got a wonderful view of the surrounding country. They found that the heliograph they had left behind was working feverishly and Harry took out a pencil and jotted down the symbols as they were flashed.

"It's in code, of course," he said, "but maybe we'll find someone who can decipher it—I know they have experts for that. It might come in handy to know what they were talking about."

"There's the other station answering!" said Dick, excitedly, after a moment. "Isn't it lucky that it's such a fine day, Harry? See—there it is, over there!"

"Let me have the glasses," said Harry, taking the binoculars from Dick. "Yes, you're right! They're on the top of a hill, just about where I thought we'd find them, too. Come on! We've got no time to waste. They're a good seven miles from here, and we've a lot more to do yet."

Below stairs the old gentleman tried to stop them. He was very curious by this time, for he had been thinking about them and it had struck him that they were too much in earnest to simply be enjoying a lark. But Harry and Dick, while they met his questions politely, refused to enlighten him.

"I'm sorry, sir," said Harry, when the old gentleman pressed him too hard. "But I really think we mustn't tell you why we're here. But if you would like to hear of it later, we'll be glad to come to see you and explain everything."

"Bless my soul!" said the old man. "When I was a boy we didn't think so much of ourselves, I can tell you! But then we didn't have any Boy Scouts, either!"

It was hard to tell from his manner whether that was intended for a compliment or not. But they waited no longer. In a trice they were on their motorcycles and off again. And when they drew near to the hilltop whence the signals had come, Harry stopped. For a moment he looked puzzled, then he smiled.

"I think I've got it!" he said. "They're clever enough to try to fool anyone who got on to their signalling. They would know what everyone would think—that they would be sending their messages to the East coast, because that is nearest to Germany. That's why they put their first station here. I'll bet they send the flashes zig-zagging all around, but that we'll find they all get east gradually. Now we'll circle around this one until we find out in what direction it is flashing, then we'll know what line we must follow. After that all we've got to do is to follow the line to some high hill or building, and we'll pick up the next station."

Their eyes were more accustomed to the work now, and they wasted very little time. This time, just as Harry had guessed, the flashes were being sent due east, and judging from the first case that the next station would be less than ten miles away, he decided to ride straight on for about that distance. He had a road map, and found that they could follow a straight line, except for one break. They did not go near the hilltop at all.

"I'd like to know what they're doing there," said Dick.

"So would I, but it's open country, and they're probably keeping a close lookout. They're really safer doing that in the open than on the roof of a house, out here in the country."

"Because they can hide the heliograph? It's portable, isn't it?"

"Yes. They could stow it away in a minute, if they were alarmed. I fancy we'll find them using hilltops now as much as they can."

"Harry, I've just thought of something. If they've planned so carefully as this, wouldn't they be likely to have country places, where they'd be less likely to be disturbed?"

"Yes, they would. You're right, Dick. Especially as we get further and further away from London. I suppose there must be plenty of places a German could buy or lease."

"And perhaps people wouldn't even know they were Germans, if they spoke good English, and didn't have an accent."

That suggestion of Dick's bore fruit. For the third station they found was evidently hidden away in a private park. It was in the outskirts of a little village, and Harry and Dick had no trouble at all in finding out all the villagers knew of the place.

"'Twas taken a year ago by a rich American gentleman, with a sight of motor cars and foreign-looking servants," they were told. "Very high and mighty he is, too—does all his buying at the stores in Lunnon, and don't give local trade any of his patronage."

The two scouts exchanged glances. Their suspicions were confirmed in a way. But it was necessary to be sure; to be suspicious was not enough for them.

"We'll have to get inside," he said under his breath to Dick. But the villager heard, and laughed.

"Easy enough, if you're friends of his," he said. "If not—look out, master! He's got signs up warning off trespassers, and traps and spring guns all over the place. Wants to be very private, and all that, he does."

"Thanks," said Harry. "Perhaps we'd better not pay him a visit, after all."

The village was a sleepy little place, one of the few spots Harry had seen to which the war fever had not penetrated. It was not on the line of the railway, and there was not even a telegraph station. By showing Colonel Throckmorton's letter, Harry and Dick could have obtained the right to search the property that they suspected. But that did not seem wise.

"I don't think the village constables here could help us much, Dick," said Harry. "They'd give everything away, and we probably wouldn't accomplish anything except to put them on their guard. I vote we wait until dark and try to find out what we can by ourselves. It's risky but even if they catch us, I don't think we need to be afraid of their doing anything."

"I'm with you," said Dick. "We'll do whatever you say."

They spent the rest of the afternoon scouting around the neighboring country on their motorcycles, studying the estate from the roads that surrounded it. Bray Park, it was called, and it had for centuries belonged to an old family, which, however, had been glad of the high rent it had been able to extract from the rich American who had taken the place.

What they saw was that the grounds seemed to be surrounded, near the wall, by heavy trees, which made it difficult to see much of what was within. But in one place there was a break, so that, looking across velvety green lawns, they could see a small part of an old and weatherbeaten grey house. It appeared to be on a rise, and to stand several stories above the ground, so that it might well be an ideal place for the establishment of a heliograph station. But Harry's suspicions were beginning to take a new turn.

"I believe this is the biggest find we've made yet, Dick," he said. "I think we'll find that if we discover what is really going on here, we'll be at the end of our task—or very near it. It's just the place for a headquarters."

"I believe it is, Harry. And if they've been so particular to keep everything about it secret, it certainly seems that there must be something important to hide," suggested Harry, thinking deeply.

"I think I'll write a letter to Colonel Throckmorton, Dick. I'll tell him about this place, and that we're trying to get in and find out what we can about it. Then, if anything happens to us, he'll know what we were doing, and he will have heard about this place, even if they catch us. I'll post it before we go in."

"That's a splendid idea, Harry. I don't see how you think of everything the way you do."

"I think it's because my father's always talking about how one ought to think of all the things that can go wrong. He says that the way he's got along in business is by never being surprised by having something unfortunate happen, and by always trying to be ready to make it as trifling as it can be."

So Harry wrote and posted his letter, taking care to word it so that it would be hard for anyone except Colonel Throckmorton to understand it. And, even after having purposely made the wording rather obscure, he put it into code. And, after that, he thought of still another precaution that might be wise.

"We won't need the credentials we've got in there to-night, Dick," he said. "Nor our copies of the code, either. We'll bury them near where we leave our motorcycles. Then when we get out we can easily get them back, and if we should be caught they won't be found on us. Remember, if we are caught, we're just boys out trespassing. Let them think we're poachers, if they like."

But even Harry could think of no more precautions after that, and they had a long and tiresome wait until they thought it was dark enough to venture within the walls.

Getting over the wall was not difficult. They had thought they might find broken glass on top, but there was nothing of the sort. Once inside, however, they speedily discovered why that precaution was not taken—and also that they had had a remarkably narrow escape. For scarcely had they dropped to the ground and taken shelter when they saw a figure, carrying a gun, approaching. It was a man making the rounds of the wall. While they watched he met another man, also armed, and turned to retrace his steps.

"They've got two men, at least—maybe a lot more, doing that," whispered Harry. "We've got to find out just how often he passes that spot. We want to know if the intervals are regular, too, so that we can calculate just when he'll be there."

Three times the man came and went, while they waited, timing him. And Harry found that he passed the spot at which they had entered every fifteen minutes. That was not exact for there was a variation of a minute or so, but it seemed pretty certain that he would pass between thirteen and seventeen minutes after the hour, and so on.

"So we'll know when it's safe to make a dash to get out," said Harry. "The first thing a general does, you know, is to secure his retreat. He doesn't expect to be beaten, but he wants to know that he can live to fight another day if he is."

"We've got to retreat, haven't we?" said Dick. "It wouldn't do us any good to stay here."

"That's so. But we've got to advance first. Now to get near that house, and see what we can find. Look out for those traps and things our friend warned us of. It looks like just the place for them. And keep to cover!"

They wormed their way forward, often crawling along. Both knew a good deal about traps and how they are set, and their common sense enabled them to see the most likely places for them. They kept to open ground, avoiding shrubbery and what looked like windfalls of branches. Before they came into full view of the house they had about a quarter of a mile to go. And it was an exciting journey.

They dared not speak to one another. For all about, though at first they could see nothing, there was the sense of impending danger. They felt that unseen eyes were watching, not for them, perhaps, but for anyone who might venture to intrude and pass the first line. Both of the scouts felt that they were tilting against a mighty force; that the organization that would perfect, in time of peace, such a system of espionage in the heart of the country of a possible enemy, was of the most formidable sort.

They stopped, at last, at the edge of the clump of thick, old trees that seemed to surround the place. Here they faced the open lawn, and Harry realized that to try to cross it was too risky. They would gain nothing by being detected. They could find out as much here by keeping their eyes and ears open, he thought, as by going forward, when they were almost sure to be detected.

"We'll stay here," he whispered to Dick, cautiously. "Dick, look over there—to the left of the house. You see where there's a shadow by that central tower? Well, to the left of that. Do you see some wires dangling there? I'm not sure."

"I think there are," whispered Dick, after a moment in which he peered through the darkness. Dick had one unusual gift. He had almost a savage's ability to see in the dark, although in daylight his sight was by no means out of the ordinary.

"Look!" he said, again, suddenly. "Up on top of the tower! There is something going up there—it's outlined against that white cloud!"

Harry followed with his eyes. And Dick was right. A long, thin pole was rising, even as they looked. Figures showed on the roof of the tower. They were busy about the pole. It seemed to grow longer as they watched. Then, suddenly, the dangling wires they had first noticed were drawn taut, and they saw a cross-piece on the long pole. And then, with a sudden rush of memory, Harry understood.

"Oh! We have struck it!" he said. "I remember now—a portable, collapsible wireless installation! I've wondered how they could use wireless, knowing that someone would be sure to pick up the signals and that the plant would be run down. But they have those poles made in sections—they could hide the whole thing. It takes very little time to set them up. This is simply a bigger copy of what they use in the field. We've got to get out!"

He looked at his watch.

"Carefully, now," he said. "We've just about got time. That sentry must be just about passing the place where we got over the wall now. By the time we get there he'll be gone, and we can slip out. We've got everything we came for, now that we've seen that!"

They started on the return journey through the woods. More than ever there seemed to be danger about them. And suddenly it reached out and gripped them—gripped Harry, at least. As he took a step his foot sank through the ground, as it seemed. The next moment he had all he could do to suppress a cry of agony as a trap closed about his ankle, wrenching it, and throwing him down.

"Go on!" he said to Dick, suppressing his pain by a great effort.

"I won't leave you!" said Dick. "I—"

"Obey orders! Don't you see you've got to go? You've got to tell them about the wireless—and about where I am! Or else how am I to get away? Perhaps if you come back quickly with help they won't find me until you come! Hurry—hurry!"

Dick understood. And, with a groan, he obeyed orders, and went.