Harry had reached Colonel Throckmorton without difficulty and before delivering Major French's message, he explained his suspicions regarding the driver.

"What's that? Eh, what's that?" asked the colonel. "Spy? This country's suffering from an epidemic of spy fever—that's what! Still—a taxicab driver, eh? Perhaps he's one of the many who's tried to overcharge me. I'll put him in the guardhouse, anyway! I'll find out if you're right later, young man!"

As a matter of fact, and as Harry surmised, Colonel Throckmorton felt that it was not a time to take chances. He was almost sure that Harry was letting his imagination run away with him, but it would be safer to arrest a man by mistake than to let him go if there was a chance that he was guilty. So he gave the order, and then turned to question Harry. The scout first gave Major French's message, and Colonel Throckmorton immediately dispatched an orderly after giving him certain whispered instructions.

"Now tell me just why you suspect your driver. Explain exactly what happened," he said. He turned to a stenographer. "Take notes of this, Johnson," he directed.

Harry told his story simply and well. When he quoted the officer's remark to the cab driver, with the German inversion, the colonel chuckled.

"'You have your way lost!' Eh?" he said, with a smile. "You're right—he was no Englishman! Go on!"

When he had finished, the colonel brought down his fist on his desk with a great blow.

"You've done very well, Fleming—that's your name?—very well, indeed," he said, heartily. "We know London is covered with spies but we had flattered ourselves that it didn't matter very much what they found, since there was no way that we could see for them to get their news to their headquarters in Germany. But now—"

He frowned thoughtfully.

"They might be able to set up a chain of signalling stations," he said. "The thing to do would be to follow them, eh? Do you think you could do that? You might use a motorcycle—know how to ride one?"

"Yes, sir," said Harry.

"Live with your parents, do you? Would they let you go? I don't think it would be very dangerous, and you would excite less suspicion than a man. See if they will let you turn yourself over to me for a few days. Pick out another scout to go with you, if you like. Perhaps two of you would be better than one. Report to me in the morning. I'll write a note to your scoutmaster—Mr. Wharton, isn't it? Right!"

As they made their way homeward, thoroughly worked up by the excitement of their adventure, Harry wondered whether his father would let him undertake this service Colonel Throckmorton had suggested. After all, he was not English, and he felt that his father might not want him to do it, although Mr. Fleming, he knew, sympathized strongly with the English in the war. He said nothing to Dick, preferring to wait until he was sure that he could go ahead with his plans.

But when he reached his house he found that things had changed considerably in his absence. Both his parents seemed worried; his father seemed especially troubled.

"Harry," he said, "the war has hit us already. I'm called home by cable, and at the same time there is word that your Aunt Mary is seriously ill. Your mother wants to be with her. I find that, by a stroke of luck, I can get quarters for your mother and myself on to-morrow's steamer. But there's no room for you. Do you think you could get along all right if you were left here? I'll arrange for supplies for the house; Mrs. Grimshaw can keep house. And you will have what money you need."

"Of course I can get along!" said Harry, stoutly. "I suppose the steamers are fearfully crowded?"

"Only about half of them are now in service," said Mr. Fleming. "And the rush of Americans who have been travelling abroad is simply tremendous. Well, if you can manage, it will relieve us greatly. I think we'll be back in less than a month. Keep out of mischief. And write to us as often as you can hear of a steamer that is sailing. If anything happens to you, cable. I'll arrange with Mr. Bruce, at the Embassy, to help you if you need him, but that ought not to be necessary."

Harry was genuinely sorry for his mother's distress at leaving him, but he was also relieved, in a way. He felt now he would not be forbidden to do his part with the scouts. He would be able to undertake what promised to be the greatest adventure that had ever come his way. He had no fear of being left alone for his training as a Boy Scout had made him too self reliant for that.

Mr. and Mrs. Fleming started for Liverpool that night. Train service throughout the country was so disorganized by the military use of the railways that journeys that in normal, peaceful times required only two or three hours were likely to consume a full day. So he went into the city of London with them and saw them off at Euston, which was full of distressed American refugees.

The Flemings found many friends there, of whose very presence in London they were ignorant, and Mr. Fleming, who, thanks to his business connections in London, was plentifully supplied with cash, was able to relieve the distress of some of them.

Many had escaped from France, Germany and Austria with only the clothes they wore, having lost all their luggage. Many more, though possessed of letters of credit or travellers' checks for considerable sums, didn't have enough money to buy a sandwich, since the banks were all closed and no one would cash their checks.

So Harry had another glimpse of the effects of war, seeing how it affected a great many people who not only had nothing to do with the fighting, but were citizens of a neutral nation. He was beginning to understand very thoroughly by this time that war was not what he had always dreamed. It meant more than fighting, more than glory.

But, after all, now that war had come, it was no time to think of such things. He had undertaken, if he could get permission, to do a certain very important piece of work. And now, by a happy accident, as he regarded it, it wasn't necessary for him to ask that permission. He was not forbidden to do any particular thing; his father had simply warned him to be careful.

So when he went home, he whistled outside of Dick Mercer's window, woke him up, and, when Dick came down into the garden, explained to him what Colonel Throckmorton wanted them to do.

"He said I could pick out someone to go with me, Dick," Harry explained. "And, of course, I'd rather have you than anyone I can think of. Will you come along?"

"Will I!" said Dick. "What do you think you'll do, Harry?"

"We may get special orders, of course," said Harry. "But I think the first thing will be to find out just where the signals from that house are being received. They must be answered, you know, so we ought to find the next station. Then, from that, we can work on to the next."

"Where do you suppose those signals go to?"

"That's what we've got to find out, Dick! But I should think, in the long run, to some place on the East coast. Perhaps they've got some way there of signalling to ships at sea. Anyhow, that's what's got to be discovered. Did you see Graves to-night?"

"No," said Dick, his lips tightening, "I didn't! But I heard about him, all right."

"How? What do you mean?"

"I heard that he'd been doing a lot of talking about you. He said it wasn't fair to have taken you and given you the honor of doing something when there were English boys who were just as capable of doing it as you."

"Oh!" said Harry, with a laugh. "Much I care what he says!"

"Much I care, either!" echoed Dick. "But, Harry, he has made some of the other chaps feel that way, too. They all like you, and they don't like him. But they do seem to think some of them should have been chosen."

"Well, it's not my fault," said Harry, cheerfully. "I certainly wasn't going to refuse. And it isn't as if I'd asked Mr. Wharton to pick me out."

"No, and I fancy there aren't many of them who would have done as well as you did to-day, either!"

"Oh, yes, they would! That wasn't anything. We'd better get to bed now. I think we ought to report just as early as we can in the morning. If we get away by seven o'clock, it won't be a bit too early."

"All right. I'll be ready. Good-night, Harry!"

"Good-night, Dick!"

Morning saw them up on time, and off to Ealing. There Colonel Throckmorton gave them their orders.

"I've requisitioned motorcycles for you," he said. "Make sure of the location of the house, so that you can mark it on an ordnance map for me. Then use your own judgment,—but find the next house. I have had letters prepared for you that will introduce you to either the mayor or the military commander in any town you reach and you will get quarters for the night, if you need them. Where do you think your search will lead you, Fleming?"

He eyed Harry sharply as he asked the question.

"Somewhere on the East coast, I think, sir," replied Harry.

"Well, that remains to be seen. Report by telegraph, using this code. It's a simplified version of the official code, but it contains all you will need to use. That is all."

Finding the house, when they started on their motorcycles, did not prove as difficult a task as Harry had feared it might. They both remembered a number of places they had marked from the cab windows, and it was not long before they were sure they were drawing near.

"I remember that hill," said Harry. "By Jove—yes, there it is! On top of that hill, do you see? We won't go much nearer. I don't want them to see us, by any chance. All we need is to notice which way they're signalling."

They watched the house for some time before there was any sign of life. And then it was only the flashes that they saw. Since the previous day some sort of cover had been provided for the man who did the signalling.

"What do you make of it, Dick?" asked Harry eagerly, after the flashing had continued for some moments.

"It looks to me as if they were flashing toward the north and a little toward the west," said Dick, puzzled.

"That's the way it seems to me, too," agreed Harry. "That isn't what we expected, either, is it?"

"Of course we can't be sure."

"No, but it certainly looks that way. Well, we can't make sure from here, but we've got to do it somehow. I tell you what. We'll circle around and get northwest of the house. Then we ought to be able to tell a good deal better. And if we get far enough around, I don't believe they'll see us, or pay any attention to us if they do."

So they mounted their machines again, and in a few moments were speeding toward a new and better spot from which to spy on the house. But this, when they reached it, only confirmed their first guess. The signals were much more plainly visible here, and it was obvious now, as it had not been before, that the screen they had noticed had been erected as much to concentrate the flashes and make them more easily visible to a receiving station as to conceal the operator. So they turned and figured a straight line as well as they could from the spot where the flashes were made. Harry had a map with him, and on this he marked, as well as he could, the location of the house. Then he drew a line from it to the northwest.

"The next station must be on this line somewhere," he said. "We'll stick to it. There's a road, you see, that we can follow that's almost straight. And as soon as we come to a high building we ought to be able to see both flashes—the ones that are being sent from that house and the answering signals. Do you see?"

"Yes, that'll be fine!" said Dick. "Come on!"

"Not so fast!" said a harsh voice behind them. They spun around, and there, grinning a little, but looking highly determined and dangerous, was the same man they had seen the day before, and who had questioned them, when the tire of their taxicab blew out! But now he was not in uniform, but in a plain suit of clothes.

"So you are spying on my house, are you?" he said. "And you lied to me yesterday! No troops were sent to Croydon at all!"

"Well, you hadn't any business to ask us!" said Dick, pluckily. "If you hadn't asked us any questions, we'd have told you no lies."

"I think perhaps you know too much," said the spy, nodding his head. "You had better come with me. We will look after you in this house that interests you so greatly."

He made a movement forward. His hand dropped on Dick's shoulder. But as it did so Harry's feet left the ground. He aimed for the spy's legs, just below the knee, and brought him to the ground with a beautiful diving tackle—the sort he had learned in his American football days. It was the one attack of all others that the spy did not anticipate, if, indeed, he looked for any resistance at all. He wasn't a football player, so he didn't know how to let his body give and strike the ground limply. The result was that his head struck a piece of hard ground with abnormal violence, and he lay prone and very still.

"Oh, that was ripping, Harry!" cried Dick. "But do you think you've killed him?"

"Killed him? No!" said Harry, with a laugh. "He's tougher than that, Dick!"

But he looked ruefully at the spy.

"I wish I knew what to do with him," he said. "He'll come to in a little while. But—"

"We can get away while he's still out," said Dick, quickly. "He can't follow us and we can get such a start with our motorcycles—"

"Yes, but he'll know their game is up," said Harry. "Don't you see, Dick? He'll tell them they're suspected—and that's all they'll need in the way of warning. When men are doing anything as desperate as the sort of work they're up to in that house, they take no more chances than they have to. They'd be off at once, and start up somewhere else. We only stumbled on this by mere accident—they might be able to work for weeks if they were warned."

"Oh, I never thought of that! What are we to do, then?"

"I wish I knew whether anyone saw us from the house! If they didn't—! Well, we'll have to risk that. Dick, do you see that house over there? It's all boarded up—it must be empty."

"Yes, I see it." Dick caught Harry's idea at once this time, and began measuring with his eye the distance to the little house of which Harry had spoken. "It's all down hill—I think we could manage it all right."

"We'll try it, anyhow," said Harry. "But first we'd better tie up his hands and feet. He's too strong for the pair of us, I'm afraid, if he should come to."

Once that was done, they began to drag the spy toward the house. Half carrying, half pulling, they got him down the slope, and with a last great effort lifted him through a window, which, despoiled of glass, had been boarded up. They were as gentle as they could be, for the idea of hurting a helpless man, even though he was a spy, went against the grain. But—

"We can't be too particular," said Harry. "And he brought it on himself. I'm afraid he'll have worse than this to face later on."

They dumped him through the window, from which they had taken the boards. Then they made their own way inside, and Harry began to truss up the prisoner more scientifically. He understood the art of tying a man very well indeed, for one of the games of his old scout patrol had involved tying up one scout after another to see if they could free themselves. And when he had done, he stepped back with a smile of satisfaction.

"I don't believe he'll get himself free very soon," he said. "He'll be lucky if that knock on the head keeps him unconscious for a long time, because he'll wake up with a headache, and if he stays as he is, he won't know how uncomfortable he is."

"Are we going to leave him like that, Harry?"

"We've got to, Dick. But he'll be all right. I am going to telephone to Colonel Throckmorton and tell him to send here for him, but to do so at night, and so that no one will notice. He won't starve or die of thirst. I can easily manage to describe this place so that whoever the colonel sends will find it. Come on!"

They went back to their cycles and rode on until they came to a place where they could telephone. Harry explained guardedly, and they went on.