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 clue 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 clue! 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 clue 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 clue, 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 clue 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 clue 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.