Tom Swift was so overjoyed and excited that for a few moments he capered about, inside the booth, and outside, knocking against his chum Ned, clapping him on the back, and doing all manner of boyish "stunts."

"It's a success, Ned! I've struck it!" cried Tom, in delight.

"Ouch! You struck me, you mean!" replied Ned, rubbing his shoulder, where the young inventor had imparted a resounding blow of joy.

"What of it?" exclaimed Tom. "My apparatus works! I can send a picture by telephone! It's great, Ned!"

"But I don't exactly understand how it happened," said Ned, in some bewilderment, as he gazed at the selenium plate.

"Neither do I," admitted Tom, when he had somewhat calmed down. "That is, I don't exactly understand what made the thing succeed now, when it wouldn't work for me a little while ago. But I've got to go into that. I'll have to interview that rascal Eradicate, and learn what he did when he played that trick on Koku. Yes, and I'll have to see Koku, too. We've got to get at the bottom of this, Ned."

"I suppose so. You've got your hands full, Tom, with your photo telephone, and the disappearance of Mr. Damon."

"Yes, and my own airship, too. I must get after that. Whew! A lot of things to do! But I like work, Ned. The more the better."

"Yes, that's like you, Tom. But what are you going to get at first?"

"Let me see; the telephone, I think. I'll have Rad and Koku in here and talk to them. I say, you Eradicate!" he called out of the door of the shop, as he saw the colored man going past, holding his shocked arm tenderly.

"Yas, sah, Massa Tom, I'se comin'! What is it yo' all wants, Massa Tom?"

"I want you to show me exactly what you did to the wires, and other things in here, when you played that Angel Gabriel trick on your partner Koku."

"Partner! He ain't mah partner!" exclaimed Eradicate with a scowl, for there was not the best of feeling between the two. Eradicate had served in the Swift family many years, and he rather resented the coming of the giant, who performed many services formerly the province of the colored man.

"Well, never mind what he is, Rad," laughed Tom. "You just show me what you did. Come now, something happened in here, and I want to find out what it was."

"Oh, suffin done happened all right, Massa Tom. Yas, sah! Suffin done happened!" cried Eradicate, with such odd emphasis that Tom and Ned both laughed.

"An' suffin happened to me," went on the colored man, rubbing his shocked arm.

"Well, tell us about it," suggested Tom.

"It was dish yeah way," proceeded Eradicate. And he told more in detail how, seeing Koku cleaning and sweeping out the other telephone booth, he had thought of the trick to play on him. Both telephones had what are called "amplifiers" attached, that could be switched on when needed. These amplifiers were somewhat like the horn of a phonograph--they increased, or magnified the sound, so that one could hear a voice from any part of the shop, and need not necessarily have the telephone receiver at his ear.

Seeing Koku near the instrument, Eradicate had switched on the amplifier, and had called into his instrument, trying to scare the giant. And he did startle Koku, for the loud voice, coming so suddenly, sent the giant out of the booth on the run.

"But you must have done something else," insisted Tom. "Look here, Rad," and the young inventor pointed to the picture on the plate.

"Mah gracious sakes!" gasped the colored man. "Why dat's Koku hisse'f!" and he looked in awe at the likeness.

"That's what you did, Rad!"

"Me? I done dat? No, sah, Massa Tom. I neber did! No, sah!" Eradicate spoke emphatically.

"Yes you did, Rad. You took that picture of Koku over my photo telephone, and I want you to show me exactly what you did--what wires and switches you touched and changed, and all that."

"Yo--yo' done say I tuck dat pishure, Massa Tom?"

"You sure did, Rad."

"Well--well, good land o' massy! An' I done dat!"

Eradicate stared in wonder at the image of the giant on the plate, and shook his head doubtingly.

"I--I didn't know I could do it. I never knowed I had it in me!" he murmured.

Tom and Ned laughed long and loud, and then the young inventor said:

"Now look here, Rad. You've done me a mighty big service, though you didn't know it, and I want to thank you. I'm sorry about your arm, and I'll have the doctor look at it. But now I want you to show me all the things you touched when you played that joke on Koku. In some way you did what I haven't been able to do, You took the picture. There's probably just one little thing I've overlooked, and you stumbled on it by accident. Now go ahead and show me."

Eradicate thought for a moment, and then said:

"Well, I done turned on de current, laik I seen you done, Massa Tom."

"Yes, go on. You connected the telephone."

"Yas, sah. Den I switched on that flyer thing yo' all has rigged up."

"You switched on the amplifier, yes. Go on."

"An'--an' den I plugged in dish year wire," and the colored man pointed to one near the top of the booth.

"You switched on that wire, Rad! Why, great Scott, man! That's connected to the arc light circuit--it carries over a thousand volts. And you switched that into the telephone circuit?"

"Dat's what I done did, Massa Tom; yas, sah!"

"What for?"

"Why, I done want t' make mah voice good an' loud t' skeer dat rascal Koku!"

Tom stared at the colored man in amazement.

"No wonder you got a shock!" exclaimed the young inventor. "You didn't get all the thousand volts, for part of it was shunted off; but you got a good charge, all right. So that's what did the business; eh? It was the combination of the two electrical circuits that sent the photograph over the wire."

"I understand it now, Rad; but you did more than I've been able to do. I never, in a hundred years, would have thought of switching on that current. It never occurred to me. But you, doing it by accident, brought out the truth. It's often that way in discoveries. And Koku was standing in the other telephone booth, near the plate there, when you switched in this current, Rad?"

"Yas, sah, Massa Tom. He were. An' yo' ought t' see him hop when he heard mah voice yellin' at him. Ha! ha! ha!"

Eradicate chuckled at the thought. Then a pain in his shocked arm made him wince. A wry look passed over his face.

"Yas, sah, Koku done jump about ten feet," he said. "An'--an' den I jump too. Ain't no use in denyin' dat fact. I done jump when I got dat shock!"

"All right, Rad. You may go now. I think I'm on the right track!" exclaimed Tom. "Come on, Ned, we'll try some experiments, and we'll see what we can do."

"No shocks though--cut out the shocks, Tom," stipulated his chum.

"Oh, sure! No shocks! Now let's get busy and improve on Eradicate's Angel Gabriel system."

Tom made a quick examination of the apparatus.

"I understand it, I think," he said. "Koku was near the plate in the other booth when Rad put on the double current. There was a light there, and in an instant his likeness was sent over the wire, and imprinted on this plate. Now let's see what we can do. You go to that other booth, Ned. I'll see if I can get your picture, and send you mine. Here, take some extra selenium plates along. You know how to connect them."

"I think so," answered Ned.

"This image is really too faint to be of much use," went on Tom, as he looked at the one of Koku. "I think I can improve on it. But we're on the right track."

A little later Ned stood in the other booth, while Tom arranged the wires, and made the connections in the way accidently discovered by Eradicate. The young inventor had put in a new plate, carefully putting away the one with the picture of the giant, This plate could be used again, when the film, into which the image was imprinted, had been washed off.

"All ready, Ned," called Tom, over the wire, when he was about to turn the switch. "Stand still, and I'll get you."

The connection was made, and Tom uttered a cry of joy. For there, staring at him from the plate in front of him was the face of Ned.

It was somewhat reduced in size, of course, and was not extra clear, but anyone who knew Ned could have told he was at the other end of the wire.

"Do you get me, Tom?" called Ned, over the telephone.

"I sure do! Now see if you can get me."

Tom made other connections, and then looked at the sending plate of his instrument, there being both a sending and receiving plate in each booth, just as there was a receiver and a transmitter to the telephone.

"Hurray! I see you, Tom!" cried Ned, over the wire. "Say, this is great!"

"It isn't as good as I want it," went on Tom. "But it proves that I'm right. The photo telephone is a fact, and now persons using the wire can be sure of the other person they are conversing with. I must tell dad. He wouldn't believe I could do it!"

And indeed Mr. Swift was surprised when Tom proved, by actual demonstration, that a picture could be sent over the wire.

"Tom, I congratulate you!" declared the aged inventor. "It is good news!"

"Yes, but we have bad news of Mr. Damon," said Tom, and he told his father of the disappearance of the eccentric man. Mr. Swift at once telephoned his sympathy to Mrs. Damon, and offered to do anything he could for her.

"But Tom can help you more than I can," he said. "You can depend on Tom."

"I know that," replied Mrs. Damon, over the wire.

And certainly Tom Swift had many things to do now. He hardly knew at what to begin first, but now, since he was on the right road in regard to his photo telephone, he would work at improving it.

And to this end he devoted himself, after he had sent out a general alarm to the police of nearby towns, in regard to the disappearance of Mr. Damon. The airship clew, he believed, as did the police, would be a good one to work on.

For several days after this nothing of moment occurred. Mr. Damon could not be located, and Tom's airship might still be sailing above the clouds as far as getting any trace of it was concerned.

Meanwhile the young inventor, with the help of Ned, who was given a leave of absence from the bank, worked hard to improve the photo telephone.

"Now Ned, we'll try again. I'm going to use a still stronger current, and this is the most sensitive selenium plate I've turned out yet. We'll see if we can't get a better likeness of you--one that will be plainer."

It was Tom Swift who was speaking, and he and his chum had just completed some hard work on the new photo telephone. Though the apparatus did what Tom had claimed for it, still he was far from satisfied. He could transmit over the wire the picture of a person talking at the telephone, but the likeness was too faint to make the apparatus commercially profitable.

"It's like the first moving pictures," said Tom. "They moved, but that was about all they did."

"I say," remarked Ned, as he was about to take his place in the booth where the telephone and apparatus were located, "this double-strength electrical current you're speaking of won't shock me; will it? I don't want what happened to Eradicate to happen to me, Tom."

"Don't worry. Nothing will happen. The trouble with Rad was that he didn't have the wires insulated when he turned that arc current switch by mistake--or, rather, to play his joke. But he's all right now."

"Yes, but I'm not going to take any chances," insisted Ned. "I want to be insulated myself."

"I'll see to that," promised Tom. "Now get to your booth."

For the purpose of experiments Tom had strung a new line between two of his shops, They were both within sight, and the line was not very long; but, as I have said, Tom knew that if his apparatus would work over a short distance, it would also be successful over a long one, provided he could maintain the proper force of current, which he was sure could be accomplished.

"And if they can send pictures from Monte Carlo to Paris I can do the same," declared Tom, though his system of photo telephony was different from sending by a telegraph system--a reproduction of a picture on a copper plate. Tom's apparatus transmitted the likeness of the living person.

It took some little time for the young inventor, and Ned working with him, to fix up the new wires and switch on the current. But at last it was complete, and Ned took his place at one telephone, with the two sensitive plates before him. Tom did the same, and they proceeded to talk over the wire, first making sure that the vocal connection was perfect.

"All ready now, Ned! We'll try it," called Tom to his chum, over the wire. "Look straight at the plate. I want to get your image first, and then I'll send mine, if it's a success."

Ned did as requested, and in a few minutes he could hear Tom exclaim, joyfully:

"It's better, Ned! It's coming out real clear. I can see you almost as plainly as if you were right in the booth with me. But turn on your light a little stronger."

Tom could hear, through the telephone, his chum moving about, and then he caught a startled exclamation.

"What's the matter?" asked Tom anxiously.

"I got a shock!" cried Ned. "I thought you said you had this thing fixed. Great Scott, Tom! It nearly yanked the arm off me! Is this a joke?"

"No, old man. No, of course not! Something must be wrong. I didn't mean that. Wait, I'll take a look. Say, it does seem as if everything was going wrong with this invention. But I'm on the right track, and soon I'll have it all right. Wait a second. I'll be right over."

Tom found that it was only a simple displacement of a wire that had given Ned a shock, and he soon had this remedied.

"Now we'll try again," he said. This time nothing wrong occurred, and soon Tom saw the clearest image he had yet observed on his telephone photo plate.

"Switch me on now, Ned," he called to his chum, and Ned reported that he could see Tom very plainly.

"So far--so good," observed Tom, as he came from the booth. "But there are several things I want yet to do."

"Such as what?" questioned Ned.

"Well, I want to arrange to have two kinds of pictures come over the wire. I want it so that a person can go into a booth, call up a friend, and then switch on the picture plate, so he can see his friend as well as talk to him. I want this plate to be like a mirror, so that any number of images can be made to appear on it. In that way it can be used over and over again. In fact it will be exactly like a mirror, or a telescope. No matter how far two persons may be apart they can both see and talk to one another."

"That's a big contract, Tom."

"Yes, but you've seen that it can be done. Then another thing I want to do is to have it arranged so that I can make a photograph of a person over a wire."

"Meaning what?"

"Meaning that if a certain person talks to me over the wire, I can turn my switch, and get a picture of him here at my apparatus connected with my telephone. To do that I'll merely need a sending apparatus at the other end of the telephone line--not a receiving machine."

"Could you arrange it so that the person who was talking to you would have his picture taken whether he wanted it or not?" asked Ned.

"Yes, it might be done," spoke Tom, thoughtfully. "I could conceal the sending plate somewhere in the telephone booth, and arrange the proper light, I suppose."

"That might be a good way in which to catch a criminal," went on Ned. "Often crooks call up on the telephone, but they know they are safe. The authorities can't see them--they can only hear them. Now if you could get a photograph of them while they were telephoning--"

"I see!" cried Tom, excitedly. "That's a great idea! I'll work on that, Ned."

And, all enthusiasm, Tom began to plan new schemes with his photo telephone.

The young inventor did not forget his promise to help Mrs. Damon. But he could get absolutely no clew to her husband's whereabouts. Mr. Damon had completely and mysteriously disappeared. His fortune, too, seemed to have been swallowed up by the sharpers, though lawyers engaged by Tom could fasten no criminal acts on Mr. Peters, who indignantly denied that he had done anything unlawful.

If he had, he had done it in such a way that he could not be brought to justice. The promoter was still about Shopton, as well groomed as ever, with his rose in his buttonhole, and wearing his silk hat. He still speeded up and down Lake Carlopa in his powerful motor boat. But he gave Tom Swift a wide berth.

Late one night, when Tom and Ned had been working at the new photo telephone, after all the rest of the household had retired, Tom suddenly looked up from his drawings and exclaimed:

"What's that?"

"What's what?" inquired Ned.

"That sound? Don't you hear it? Listen!"

"It's an airship--maybe yours coming back!" cried the young banker.

As he spoke Ned did hear, seemingly in the air above the house, a curious, throbbing, pulsating sound.

"That's so! It is an airship motor!" exclaimed Tom. "Come on out!"

Together they rushed from the house, but, ere they reached the yard, the sound had ceased. They looked up into the sky, but could see nothing, though the night was light from a full moon.

"I certainly heard it," said Tom.

"So did I," asserted Ned. "But where is it now?"

They advanced toward the group of work-buildings. Something showing white in the moonlight, before the hangar, caught Ned's eyes.

"Look!" he exclaimed. "There's an airship, Tom!"

The two rushed over to the level landing place before the big shed. And there, as if she had just been run out for a flight, was the Eagle. She had come back in the night, as mysteriously as she had been taken away.

"Well, this gets me!" exclaimed Tom.

"It sure is strange," agreed Ned. "How did she come here?"

"She didn't come alone--that's sure," went on Tom. "Someone brought her here, made a landing, and got away before we could get out."

The two chums were standing near the Eagle, which had come back so mysteriously.

"Just a couple of seconds sooner and we'd have seen who brought her here," went on Tom. "But they must have shut off the motor some distance up, and then they volplaned down. That's why we didn't hear them."

Ned went over and put his hand on the motor.

"Ouch!" he cried, jumping back. "It's hot!"

"Showing that she's been running up to within a few minutes ago," said Tom. "Well, as I said before, this sure does get me. First these mysterious men take my airship, and then they bring her back again, without so much as thanking me for the use of her."

"Who in the world can they be?" asked Ned.

"I haven't the least idea. But I'm going to find out, if it's at all possible. We'll look the machine over in the morning, and see if we can get any clews. No use in doing that now. Come on, we'll put her back in the hangar."

"Say!" exclaimed Ned, as a sudden idea came to him. "It couldn't be Mr. Damon who had your airship; could it, Tom?"

"I don't know. Why do you ask that?"

"Well, he might have wanted to get away from his enemies for a while, and he might have taken your Eagle, and--"

"Mr. Damon wouldn't trail along with a crowd like the one that took away my airship," said Tom, decidedly. "You've got another guess coming, Ned. Mr. Damon had nothing to do with this."

"And yet the night he disappeared an airship was heard near his house."

"That's so. Well, I give up. This is sure a mystery. We'll have a look at it in the morning. One thing I'll do, though, I'll telephone over to Mr. Damon's house and see if his wife has heard any news. I've been doing that quite often of late, so she won't think anything of it. In that way we can find out if he had anything to do with my airship. But let's run her into the shed first."

This was done, and Koku, the giant, was sent to sleep in the hangar to guard against another theft. But it was not likely that the mysterious men, once having brought the airship back, would come for it again.

Tom called up Mrs. Damon on the telephone, but there was no news of the missing man. He expressed his sympathy, and said he would come and see her soon. He told Mrs. Damon not to get discouraged, adding that he, and others, were doing all that was possible. But, in spite of this, Mrs. Damon, naturally, did worry.

The next morning the two chums inspected the airship, so mysteriously returned to them. Part after part they went over, and found nothing wrong. The motor ran perfectly, and there was not so much as a bent spoke in the landing wheels. For all that could be told by an inspection of the craft she might never have been out of the hangar.

"Hello, here's something!" cried Tom, as he got up from the operator's seat, where he had taken his place to test the various controls.

"What is it?" asked Ned.

"A button. A queer sort of a button. I never had any like that on my clothes, and I'm sure you didn't. Look!" and Tom held out a large, metal button of curious design.

"It must have come off the coat of one of the men who had your airship, Tom," said his chum. "Save it. You may find that it's a clew."

"I will. No telling what it may lead to. Well, I guess that's all we can find."

And it was. But Tom little realized what a clew the button was going to be. Nothing more could be learned by staring at the returned airship, so he and Ned went back to the house.

Tom Swift had many things to do, but his chief concern was for the photo telephone. Now that he was near the goal of success he worked harder than ever. The idea Ned had given him of being able to take the picture of a person at the instrument--without the knowledge of that person--appealed strongly to Tom.

"That's going to be a valuable invention!" he declared, but little he knew how valuable it would prove to him and to others.

It was about a week later when Tom was ready to try the new apparatus. Meanwhile he had prepared different plates, and had changed his wiring system. In the days that had passed nothing new had been learned concerning the whereabouts of Mr. Damon, nor of the men who had so mysteriously taken away Tom's airship.

All was in readiness for the trial. Tom sent Ned to the booth that he had constructed in the airship hangar, some distance away from the house. The other booth Tom had placed in his library, an entirely new system of wires being used.

"Now Ned," explained Tom, "the idea is this! You go into that booth, just as if it were a public one, and ring me up in the regular way. Of course we haven't a central here, but that doesn't matter. Now while I'm talking to you I want to see you. You don't know that, of course."

"The point is to see if I can get your picture while you're talking to me, and not let you know a thing about it."

"Think you can do it, Tom?"

"I'm going to try. We'll soon know. Go ahead."

A little later Ned was calling up his chum, as casually as he could, under the circumstances.

"All right!" called Tom to his chum. "Start in and talk. Say anything you like--it doesn't matter. I want to see if I can get your picture. Is the light burning in your booth?"

"Yes, Tom."

"All right then. Go ahead."

Ned talked of the weather--of anything. Meanwhile Tom was busy. Concealed in the booth occupied by Ned was a sending plate. It could not be seen unless one knew just where to look for it. In Tom's booth was a receiving plate.

The experiment did not take long. Presently Tom called to Ned that he need stay there no longer.

"Come on to the house," invited the young inventor, "and we'll develope this plate." For in this system it was necessary to develope the receiving plate, as is done with an ordinary photographic one. Tom wanted a permanent record.

Eagerly the chums in the dark room looked down into the tray containing the plate and the developing solution.

"Something's coming out!" cried Ned, eagerly.

"Yes! And it's you!" exclaimed Tom. "See, Ned, I got your picture over the telephone. Success! I've struck it! This is the best yet!"

At that moment, as the picture came out more and more plainly, someone knocked on the door of the dark room.

"Who is it?" asked Tom.

"Gen'man t' see you," said Eradicate. "He say he come from Mistah Peters!"

"Mr. Peters--that rascally promoter!" whispered Tom to his chum. "What does this mean?"

Tom Swift and his chum looked at one another strangely for a moment in the dim, red light of the dark room. Then the young inventor spoke:

"I'm not going to see him. Tell him so, Rad!"

"Hold on a second," suggested Ned. "Maybe you had better see him, Tom. It may have something to with Mr. Damon's lost fortune."

"That's so! I didn't think of that. And I may get a clew to his disappearance, though I don't imagine Peters had anything to do with that. Wait, Rad. Tell the gentleman I'll see him. Did he give any name, Rad?"

"Yas, sah. Him done say him Mistah Boylan."

"The same man who called to see me once before, trying to get me to do some business with Peters," murmured Tom. "Very well, I'll see him as soon as this picture is fixed. Tell him to wait, Rad."

A little later Tom went to where his caller awaited in the library. This time there were no plans to be looked at, the young inventor having made a practice of keeping all his valuable papers locked in a safe.

"You go into the next room, Ned," Tom had said to his chum. "Leave the door open, so you can hear what is said."

"Why, do you think there'll be trouble? Maybe we'd better have Koku on hand to--"

"Oh, no, nothing like that," laughed Tom. "I just want you to listen to what's said so, if need be, you can be a witness later. I don't know what their game is, but I don't trust Peters and his crowd. They may want to get control of some of my patents, and they may try some underhanded work. If they do I want to be in a position to stop them."

"All right," agreed Ned, and he took his place.

But Mr. Boylan's errand was not at all sensational, it would seem. He bowed to Tom, perhaps a little distantly, for they had not parted the best of friends on a former occasion.

"I suppose you are surprised to see me," began Mr. Boylan.

"Well, I am, to tell the truth," Tom said, calmly.

"I am here at the request of my employer, Mr. Peters," went on the caller. "He says he is forming a new and very powerful company to exploit airships, and he wants to know whether you would not reconsider your determination not to let him do some business for you."

"No, I'm afraid I don't care to go into anything like that," said Tom.

"It would be a good thing for you," proceeded Mr. Boylan, eagerly. "Mr. Peters is able to command large capital, and if you would permit the use of your airships--or one of them--as a model, and would supervise the construction of others, we could confidently expect large sales. Thus you would profit, and I am frank to admit that the company, and Mr. Peters, also, would make money. Mr. Peters is perfectly free to confess that he is in business to make money, but he is also willing to let others share with him. Come now, what do you say?"

"I am sorry, but I shall have to say the same thing I said before," replied Tom. "Nothing doing!"

Mr. Boylan glanced rather angrily at the young inventor, and then, with a shrug of his shoulders, remarked:

"Well, you have the say, of course. But I would like to remind you that this is going to be a very large airship company, and if your inventions are not exploited some others will be. And Mr. Peters also desired me to say that this is the last offer he would make you."

"Tell him," said Tom, "that I am much obliged, but that I have no business that I can entrust to him. If he wishes to make some other type of airship, that is his affair. Good-day."

As Mr. Boylan was going out Tom noticed a button dangling from the back of his caller's coat. It hung by a thread, being one of the pair usually sewed on the back of a cutaway garment.

"I think you had better take off that button before it falls," suggested Tom. "You may lose it, and perhaps it would be hard to match."

"That's so. Thank you!" said Mr. Boylan. He tried to reach around and get it, but he was too stout to turn easily, especially as the coat was tight-fitting.

"I'll get it for you," offered Tom, as he pulled it off. "There is one missing, though," he said, as he handed the button to the man. And then Tom started as he saw the pattern of the one in his hand.

"One gone? That's too bad," murmured Mr. Boylan. "Those buttons were imported, and I doubt if I can replace them. They are rather odd."

"Yes," agreed Tom, gazing as if fascinated at the one he still held. "They are rather odd."

And then, as he passed it over, like a flash it came to him where he had seen a button like that before. He had found it in his airship, which had been so mysteriously taken away and returned.

Tom could hardly restrain his impatience until Mr. Boylan had gone. The young inventor had half a notion to produce the other button, matching the one he had just pulled off his visitor's coat, and tell where he had found it. But he held himself back. He wanted to talk first to Ned.

And, when his chum came in, Tom cried:

"Ned, what do you think? I know who had my airship!"

"How?" asked Ned, in wonder.

"By that button clew! Yes, it's the same kind--they're as alike as twins!" and Tom brought out the button which he had put away in his desk. "See, Boylan had one just like this on the back of his coat. The other was missing. Here it is--it was in the seat of my airship, where it was probably pulled off as he moved about. Ned, I think I've got the right clew at last."

Ned said nothing for several seconds. Then he remarked slowly:

"Well, Tom, it proves one thing; but not the other."

"What do you mean?"

"I mean that it may be perfectly true that the button came off Mr. Boylan's coat, but that doesn't prove that he wore it. You can be reasonably sure that the coat was having a ride in your Eagle, but was Boylan in the coat? That's the question."

"In the coat? Of course he was in it!" cried Tom.

"You can't be sure. Someone may have borrowed his coat to take a midnight ride in the airship."

"Mr. Boylan doesn't look to be the kind of a man who would lend his clothes," remarked Tom.

"You never can tell. Someone may have borrowed it without his knowledge. You'd better go a bit slow, Tom."

"Well, maybe I had. But it's a clew, anyhow."

Ned agreed to this.

"And all I've got to do is to find out who was in the coat when it was riding about in my airship," went on Tom.

"Yes," said Ned, "and then maybe you'll have some clew to the disappearance of Mr. Damon."

"Right you are! Come on, let's get busy!"

"As if we hadn't been busy all the while!" laughed Ned. "I'll lose my place at the bank if I don't get back soon."

"Oh, stay a little longer--a few days," urged Tom. "I'm sure that something is going to happen soon. Anyhow my photo telephone is about perfected. But I've just thought of another improvement."

"What is it?"

"I'm going to arrange a sort of dictaphone, or phonograph, so I can get a permanent record of what a person says over the wire, as well as get a picture of him saying it. Then everything will be complete. This last won't be hard to do, as there are several machines on the market now, for preserving a record of telephone conversations. I'll make mine a bit different, though."

"Tom, is there any limit to what you're going to do?" asked Ned, admiringly.

"Oh, yes, I'm going to stop soon, and retire," laughed the young inventor.

After talking the matter over, Tom and his chum decided to wait a day or so before taking any action in regard to the button clew to the takers of the airship. After all, no great harm had been done, and Tom was more anxious to locate Mr. Damon, and try to get back his fortune, as well as to perfect his photo telephone, than he was to discover those who had helped themselves to the Eagle.

Tom and Ned put in some busy days, arranging the phonograph attachment. It was easy, compared to the hard work of sending a picture over the wire. They paid several visits to Mrs. Damon, but she had no news of her missing husband, and, as the days went by, she suffered more and more under the strain.

Finally Tom's new invention was fully completed. It was a great success, and he not only secured pictures of Ned and others over the wire, as he talked to them, but he imprinted on wax cylinders, to be reproduced later, the very things they said.

It was a day or so after he had demonstrated his new attachment for the first time, that Tom received a most urgent message from Mrs. Damon.

"Tom," she said, over the telephone, "I wish you would call. Something very mysterious has happened."

"Mr. Damon hasn't come back; has he?" asked Tom eagerly.

"No--but I wish I could say he had. This concerns him, however. Can you come?"

"I'll be there right away."

In his speedy monoplane Tom soon reached Waterford. Ned did not accompany him this time.

"Now what is it, Mrs. Damon?" asked the young inventor.

"About half an hour before I called you," she said, "I received a mysterious message."

"Who brought it?" asked Tom quickly.

"No one. It came over the telephone. Someone, whose voice I did not know, said to me: 'Sign the land papers, and send them to us, and your husband will be released.'"

"That message came over the wire?" cried Tom, excitedly.

"Yes," answered Mrs. Damon. "Oh, I am so frightened! I don't know what to do!" and the lady burst into tears.

Tom Swift, for the moment, did not know what to do. It was a strange situation, and one he had never thought of. What did the mysterious message mean? He must think it all out, and plan some line of action. Clearly Mrs. Damon was not able to do so.

"Now let's get at this in some kind of order," suggested the youth, when Mrs. Damon had calmed herself. It was his habit to have a method about doing things. "And don't worry," he advised. "I am certain some good will come of this. It proves one thing, that's sure."

"What is it, Tom?"

"That Mr. Damon is alive and well. Otherwise the message would not have said he would be 'released.' It wasn't from anyone you know; was it?"

"No, I'm sure I never heard the voice before."

Tom paused a moment to think how useful his photo telephone and phonograph arrangement might have been in this case.

"How did the telephone call come in?" inquired the young inventor.

"In the usual way," answered Mrs. Damon. "The bell rang, and, as I happened to be near the instrument, I answered it, as I often do, when the maid is busy. A voice asked if I was Mrs. Damon, and of course I said I was. Then I heard this: 'Sign the land papers, and send them to us, and your husband will be released.'"

"Was that all?" Tom asked.

"I think so--I made a note of it at the time." Mrs. Damon looked into a small red book. "No, that wasn't all," she said, quickly. "I was so astonished, at hearing those strange words about my husband, that I didn't know what to say. Before I could ask any questions the voice went on to say, rather abruptly: 'We will call you again.'"

"That's good!" cried Tom. "I only hope they do it while I am here. Perhaps I can get some clew as to who it was called you. But was this all you heard?"

"Yes, I'm sure that was all. I had forgotten about the last words, but I see I have them written down in my note book."

"Did you ask any questions?" inquired Tom.

"Oh, indeed I did! As soon as I got over being stunned by what I heard, I asked all sorts of questions. I demanded to know who was speaking, what they meant, where they were, and all that. I begged them to tell me something of my husband."

"And what did they say?"

"Not a thing. There wasn't a sound in the telephone. The receiver was hung up, breaking the connection after that message to me--that mysterious message."

"Yes, it was mysterious," agreed Tom, thoughtfully. "I can't understand it. But didn't you try to learn from the central operator where the call had come from?"

"Oh, yes, indeed, Tom! As soon as I found out the person speaking to me had rung off, I got the girl in the exchange."

"And what did she say?"

"That the call came from an automatic pay station in a drug store in town. I have the address. It was one of those telephones where you put your money for the call in a slot."

"I see. Well, the first thing to do is for me to go to that drug store and find out, if I can, who used the telephone about that time. It's a slim chance, but we'll have to take it. Was it a man's voice, or a woman's?"

"Oh, a man's, I'm sure. It was very deep and heavy. No woman could speak like that."

"So much is settled, anyhow. Now about the land papers--what was meant?"

"I'll tell you," said Mrs. Damon. "You know part of our property--considerable land and some buildings--is in my name. Mr. Damon had it fixed so a number of years ago, in order to protect me. No one could get this property, and land, unless I signed the deeds, or agreed to sign them. Now all of Mr. Damon's fortune is tied up in some of Mr. Peters's companies. That is why my husband has disappeared."

"He didn't disappear--he was taken away against his will; I'm positive of that!" exclaimed Tom.

"Perhaps so," agreed Mrs. Damon, sadly. "But those are the papers referred to, I'm sure."

"Probably," assented Tom. "The rascals want to get control of everything--even your possessions. Not satisfied with ruining Mr. Damon, they want to make you a beggar, too. So they are playing on your fears. They promise to release your husband if you will give them the land."

"Yes, that must be it, Tom. What would you advise me to do? I am so frightened over this!"

"Do? Don't you do anything!" cried Tom. "We'll fool these rascals yet. If they got those papers they might release Mr. Damon, or they might not--fearing he would cause their arrest later. But we'll have him released anyhow, and we'll save what is left of your fortune. Put those land papers in a safe-deposit box, and let me do the rest. I'm going to catch those fellows!"

"But how, Tom? You don't know who they are. And a mere message over a telephone won't give you a clew to where they are."

"Perhaps not an ordinary message," agreed Tom. "But I'm going to try some of my new inventions. You said they told you they were going to call again?"

"That's what they said, Tom."

"Well, when they do, I want to be here. I want to listen to that message. If you will allow me, I'll take up my residence here for a while, Mrs. Damon."

"Allow you? I'll be only too glad if you will, Tom. But I thought you were going to try to get some clew from the drug store where the mysterious message came from."

"I'll let Ned Newton do that. I want to stay here."

Tom telephoned to Ned to meet him at Mrs. Damon's house, and also to bring with him certain things from the laboratory. And when Ned arrived in an auto, with various bits of apparatus, Tom put in some busy hours.

Meanwhile Ned was sent to the drug store, to see if any clews could be obtained there as to who had sent the message. As Tom had feared, nothing could be learned. There were several automatic 'phones in the place, and they were used very often during the day by the public. The drug clerks took little or no notice of the persons entering or leaving the booths, since the dropping of a coin in the slot was all that was necessary to be connected with central.

"Well, we've got to wait for the second call here," said Tom, who had been busy during Ned's absence. He had fitted to Mrs. Damon's telephone a recording wax phonograph cylinder, to get a record of the speaker's voice. And he had also put in an extension telephone, so that he could listen while Mrs. Damon talked to the unknown.

"There, I guess we're ready for them," said Tom, late that afternoon. But no queer call came in that day. It was the next morning, about ten o'clock, after Mrs. Damon had passed a restless night, that the telephone bell rang. Tom, who was on the alert, was at his auxiliary instrument in a flash. He motioned to Mrs. Damon to answer on the main wire.

"Hello," she spoke into the transmitter. "Who is this?"

"Are you Mrs. Damon?" Tom heard come over the wire in a deep voice, and by the manner in which Mrs. Damon signalled the young inventor knew that, at the other end of the line, was the mysterious man who had spoken before.

"Are you Mrs. Damon?" came the question again--rather more impatiently this time, Tom thought.

"Yes," answered the lady, glancing over at Tom. The extension telephone was in the same room. Softly Tom switched on the phonograph attachment. The little wax cylinder began to revolve noiselessly, ready to record the faintest word that came over the wire.

"You got a message from me yesterday," went on the hoarse voice. In vain Tom tried to recall whether or not he had heard it before. He could not place it.

"Who are you?" asked Mrs. Damon. She and Tom had previously agreed on a line of talk. "Tell me your name, please."

"There's no need for any names to be used," went on the unknown at the other end of the wire. "You heard what I said yesterday. Are you willing to send me those land title papers, if we release your husband?"

"But where shall I send them?" asked Mrs. Damon, to gain time.

"You'll be told where. And listen--no tricks! You needn't try to find out who I am, nor where I am. Just send those papers if you want to see your husband again."

"Oh, how is he? Tell me about him! You are cruel to keep him a prisoner like this! I demand that you release him!"

Tom had not told Mrs. Damon to say this. It came out of her own heart--she could not prevent the agonized outburst.

"Never mind about that, now," came the gruff voice over the wire. "Are you willing to send the papers?"

Mrs. Damon looked over to Tom for silent instructions. He nodded his head in assent.

"Yes, I--I will send them if you tell me where to get them to you--if you will release Mr. Damon," said the anxious wife. "But tell me who you are--and where you are!" she begged.

"None of that! I'm not looking to be arrested. You get the papers ready, and I'll let you know to-morrow, about this time, where to send them."

"Wait a minute!" called Mrs. Damon, to gain more time. "I must know just what papers you want."

"All right, I'll tell you," and he began to describe the different ones.

It took a little time for the unknown to give this information to Mrs. Damon. The man was very particular about the papers. There were trust deeds, among other things, and he probably thought that once he had possession of them, with Mrs. Damon's signature, even though it had been obtained under a threat, he could claim the property. Later it was learned that such was not the case, for Mrs. Damon, with Tom's aid, could have proved the fraud, had the scoundrels tried to get the remainder of the Damon fortune.

But at the time it seemed to the helpless woman that everything she owned would be taken from her. Though she said she did not care, as long as Mr. Damon was restored to her.

As I have said, the telephoning of the instructions about the papers took some time. Tom had counted on this, and had made his plans accordingly.

As soon as the telephone call had come in, Tom had communicated with a private detective who was in waiting, and this man had gone to the drug store whence the first call had come. He was going to try to make the arrest of the man telephoning.

But for fear the scoundrel would go to a different instrument, Tom took another precaution. This was to have one of the operators in the central exchange on the watch. As soon as Mrs. Damon's house was in connection with another telephone, the location of the latter would be noted, and another private detective would be sent there. Thus Tom hoped to catch the man at the 'phone.

Meanwhile Tom listened to the hoarse voice at the other end of the wire, giving the directions to Mrs. Damon. Tom hoped that soon there would be an arrest made.

Meanwhile the talk was being faithfully recorded on the phonograph cylinder. And, as the man talked on, Tom became aware of a curious undercurrent of sound. It was a buzzing noise, that Tom knew did not come from the instrument itself. It was not the peculiar tapping, singing noise heard in a telephone receiver, caused by induced electrical currents, or by wire trouble.

"This is certainly different," mused Tom. He was trying to recall where he had heard the noise before. Sometimes it was faint, and then it would gradually increase, droning off into faintness once more. Occasionally it was so loud that Mrs. Damon could not hear the talk about the papers, and the man would have to repeat.

But finally he came to an end.

"This is all now," he said, sharply. Tom heard the words above the queer, buzzing, humming sound. "You are keeping me too long. I think you are up to some game, but it won't do you any good, Mrs. Damon. I'll 'phone you to-morrow where to send the papers. And if you don't send them--if you try any tricks--it will be the worse for you and Mr. Damon!"

There was a click, that told of a receiver being placed back on the hook, and the voice ceased. So, also, did the queer, buzzing sound over which Tom puzzled.

"What can it have been?" he asked. "Did you hear it, Mrs. Damon?"

"What, Tom?"

"That buzzing sound."

"Yes, I heard, but I didn't know what it was. Oh, Tom, what shall I do?"

"Don't worry. We'll see if anything happened. They may have caught that fellow. If not I'll plan another scheme."

Tom's first act was to call up the telephone exchange to learn where the second call had come from. He got the information at once. The address was in the suburbs. The man had not gone to the drug store this time.

"Did the detective get out to that address?" asked Tom eagerly of the manager.

"Yes. As soon as we were certain that he was the party you wanted, your man got right after him, Mr. Swift."

"That's good, I hope he catches him!" cried the young inventor. "We'll have to wait and find out."

"He said he'd call up and let you know as soon as he reached the place," the telephone manager informed Tom.

There was nothing to do but wait, and meanwhile Tom did what he could to comfort Mrs. Damon. She was quite nervous and inclined to be hysterical, and the youth thought it wise to have a cousin, who had come to stay with her, summon the doctor.

"But, Tom, what shall I do about those papers?" Mrs. Damon asked him. "Shall I send them?"

"Indeed not!"

"But I want Mr. Damon restored to me," she pleaded. "I don't care about the money. He can make more."

"Well, we'll not give those scoundrels the satisfaction of getting any money out of you. Just wait now, I'll work this thing out, and find a way to catch that fellow. If I could only think what that buzzing sound was--"

Then, in a flash, it came to Tom.

"A sawmill! A planing mill!" he cried. "That's what it was! That fellow was telephoning from some place near a sawmill!"

The telephone rang in the midst of Tom's excited comments.

"Yes--yes!" he called eagerly. "Who is it--what is it?"

"This is Larsen--the private detective you sent."

"Oh, yes, you were at the drug store."

"Yes, Mr. Swift. Well, that party didn't call up from here."

"I know, Larsen. It was from another station. We're after him. Much obliged to you. Come on back."

Tom was sure his theory was right. The man had called up the Damon house from some telephone near a sawmill. And a little later Tom's theory was proved to be true. He got a report from the second detective. Unfortunately the man had not been able to reach the telephone station before the unknown speaker had departed.

"Was the place near a sawmill?" asked Tom, eagerly.

"It was," answered the detective over the wire. "The telephone is right next door to one. It's an automatic pay station and no one seems to have noticed who the man was who telephoned. I couldn't get a single clew. I'm sorry."

"Never mind," said Tom, as cheerfully as he could. "I think I'm on the right track now. I'm going to lay a trap for this fellow."

Troublesome problems seemed to be multiplying for Tom Swift. He admitted as much himself after the failure to capture the man who had telephoned to Mrs. Damon. He had hoped that his plan of sending detectives to the location of the telephones would succeed. Since it had not the youth must try other means.

"Now, Ned," he said to his chum, when they were on their way from Mrs. Damon's, it being impossible to do anything further there. "Now, Ned, we've got to think this thing out together."

"I'm willing, Tom. I'll do what I can."

"I know you will. Now the thing to do is to go at this thing systematically. Otherwise we'll be working around in a circle, and won't get anywhere. In the first place, let's set down what we do know. Then we'll put down what we don't know, and go after that."

"Put down what you don't know?" exclaimed Ned. "How are you going to put down a thing when you don't know it?"

"I mean we can put a question mark after it, so to speak. For instance we don't know where Mr. Damon is, but we want to find out."

"Oh, I see. Well, let's start off with the things we do know."

The two friends were at Tom's house by now, having come from Waterford in Tom's airship. After thinking over all the exciting happenings of the past few days, Tom remarked: "Now, Ned, for the things we do know. In the first place Mr. Damon is missing, and his fortune is about gone. There is considerable left to Mrs. Damon, however, but those scoundrels may get that away from her, if we don't watch out. Secondly, my airship was taken and brought back, with a button more than it had when it went away. Said button exactly matched one off Mr. Boylan's coat."

"Thirdly, Mr. Damon was either taken away or went away, in an airship--either in mine or someone else's. Fourthly, Mrs. Damon has received telephonic communications from the man, or men, who have her husband. Fifthly, Mr. Peters, either legally or illegally, is responsible for the loss of Mr. Damon's fortune. Now: there you are--for the things we do know."

"Now for the things we don't know. We don't know who has taken Mr. Damon away, nor where he is, to begin with the most important."

"Hold on, Tom, I think you're wrong," broke in Ned.

"In what way?"

"About not knowing who is responsible for the taking away of Mr. Damon. I think it's as plain as the nose on your face that Peters is responsible."

"I can't see it that way," said Tom, quickly. "I will admit that it looks as though Boylan had been in my airship, but as for Peters taking Mr. Damon away--why, Peters is around town all the while, and if he had a hand in the disappearance of Mr. Damon, do you think he'd stay here, when he knows we are working on the case? And would he send Boylan to see me if Boylan had been one of those who had a hand in it? They wouldn't dare, especially as they know I'm working on the case."

"Peters is a bad lot. I'll grant you, though, he was fair enough to pay for my motor boat. I don't believe he had anything to do with taking Mr. Damon away."

"Do you think he was the person who was talking to Mrs. Damon about the papers?"

"No, Ned. I don't. I listened to that fellow's voice carefully. It wasn't like Peters's. I'm going to put it in the phonograph, too, and let you listen to it. Then see what you say."

Tom did this, a little later. The record of the voice, as it came over the wire, was listened to from the wax cylinder, and Ned had to admit that it was not much like that of the promoter.

"Well, what's next to be done?" asked the young banker.

"I'm going to set a trap," replied Tom, with a grin.

"Set a trap?"

"Yes, a sort of mouse-trap. I'm glad my photo telephone is now perfected, Ned."

"What has that got to do with it?"

"That's going to be my trap, Ned. Here is my game. You know this fellow--this strange unknown--is going to call up Mrs. Damon to-morrow. Well, I'll be ready for him. I'm going to put in the booth where he will telephone from, one of my photo telephones--that is, the sending apparatus. In Mrs. Damon's house, attached to her telephone, will be the receiving plate, as well as the phonograph cylinder."

"When this fellow starts to talk he'll be sending us his picture, though he won't know it, and we'll be getting a record of his voice. Then we'll have him just where we want him."

"Good!" cried Ned. "But, Tom, there's a weak spot in your mouse-trap."

"What is it?"

"How are you going to know which telephone the unknown will call up from? He may go to any of a hundred, more or less."

"He might--yes. But that's a chance we've got to take. It isn't so much of a chance, though when you stop to think that he will probably go to some public telephone in an isolated spot, and, unless I'm much mistaken he will go to a telephone near where he was to-day. He knows that was safe, since we didn't capture him, and he's very likely to come back."

"But to make the thing as sure as possible, I'm going to attach my apparatus to a number of public telephones in the vicinity of the one near the sawmill. So if the fellow doesn't get caught in one, he will in another. I admit it's taking a chance; but what else can we do?"

"I suppose you're right, Tom. It's like setting a number of traps."

"Exactly. A trapper can't be sure where he is going to get his catch, so he picks out the place, or run-way, where the game has been in the habit of coming. He hides his traps about that place, and trusts to luck that the animal will blunder into one of them."

"Criminals, to my way of thinking, are a good bit like animals. They seem to come back to their old haunts. Nearly any police story proves this. And it's that on which I am counting to capture this criminal. So I'm going to fit up as many telephones with my photo and phonograph outfit, as I can in the time we have. You'll have to help me. Luckily I've got plenty of selenium plates for the sending end. I'll only need one at the receiving end. Now we'll have to go and have a talk with the telephone manager, after which we'll get busy."

"You've overlooked one thing, Tom."

"What's that, Ned?"

"Why, if you know about which telephone this fellow is going to use, why can't you have police stationed near it to capture him as soon as he begins to talk?"

"Well, I did think of that, Ned; but it won't work."

"Why not?"

"Because, in the first place this man, or some of his friends, will be on the watch. When he goes into the place to telephone there'll be a look-out, I'm sure, and he'd either put off talking to Mrs. Damon, or he'd escape before we had any evidence against him."

"You see I've got to get evidence that will stand in the courts to convict this fellow, and if he's scared off before we get that, the game will be up."

"That's what my photo telephone will do--it will get the evidence, just as a dictaphone does. In fact, I'm thinking of working it out on those lines, after I clear up this business."

"Just suppose we had detectives stationed at all the telephones near the sawmill, where this fellow would be likely to go. In the first place no one has seen him, as far as we know, so there's no telling what sort of a chap he is. And you can't go up to a perfect stranger and arrest him because you think he is the man who has spirited away Mr. Damon."

"Another thing. Until this fellow has talked, and made his offer to Mrs. Damon, to restore her husband, in exchange for certain papers, we have no hold over him."

"But he has done that, Tom. You heard him, and you have his voice down on the wax cylinder."

"Yes, but I haven't had a glimpse of his face. That's what I want, and what I'm going to get. Suppose he does go into the telephone booth, and tell Mrs. Damon an address where she is to send the papers. Even if a detective was near at hand he might not catch what was said. Or, if he did, on what ground could he arrest a man who, very likely, would be a perfect stranger to him? The detective couldn't say: 'I take you into custody for telephoning an address to Mrs. Damon.' That, in itself, is no crime."

"No, I suppose not," admitted Ned. "You've got this all thought out, Tom."

"I hope I have. You see it takes quite a combination to get evidence against a criminal--evidence that will convict him. That's why I have to be so careful in setting my trap."

"I see, Tom. Well, it's about time for us to get busy; isn't it?"

"It sure is. There's lots to do. First we'll go see the telephone people."

Tom explained to the 'phone manager the necessity for what he was about to do. The manager at once agreed to let the young inventor have a free hand. He was much interested in the photo telephone, and Tom promised to give his company a chance to use it on their lines, later.

The telephone near the sawmill was easily located. It was in a general store, and the instrument was in a booth. To this instrument Tom attached his sending plate, and he also substituted for the ordinary incandescent light, a powerful tungsten one, that would give illumination enough to cause the likeness to be transmitted over the wire.

The same thing was done to a number of the public telephones in that vicinity, each one being fitted up so that the picture of whoever talked would be transmitted over the wire when Tom turned the switch. To help the plan further the telephone manager marked a number of other 'phones, "Out of Order," for the time being.