Ned Newton never knew exactly how he got out of the telephone booth. He seemed to give but one jump, tearing the clamped receiver from his ear, and almost upsetting the photo apparatus in his mad rush to help Tom. Certain it is, however, that he did get out, and a few seconds later he was speeding toward the shop where Tom had taken his position in a booth.

Ned burst in, crying out:

"Tom! What is it? What happened? What's the matter?"

There was no answer. Fearing the worst, Ned hurried to the small booth, in one corner of the big, dimly lighted shop. He could see Tom's lamp burning in the telephone compartment,

"Tom! Tom!" called the young banker.

Still there was no answer, and Ned, springing forward, threw open the double, sound-proof door of the booth. Then he saw Tom lying unconscious, with his head and arms on the table in front of him, while the low buzzing of the electrical apparatus in the transmitting box told that the current had not been shut off.

"Tom! Tom!" cried Ned in his chum's ear He shook him by the shoulder,

"Are you hurt? What is the matter?"

The young inventor seemed unconscious, and for a moment Ned had a wild idea that Tom had been shocked to death, possibly by some crossed live wire coming in contact with the telephone circuit.

"But that couldn't have happened, or I'd have been shocked myself," mused Ned.

Then he became aware of a curious, sweet, sickish odor in the booth. It was overpowering. Ned felt himself growing dizzy.

"I have it--chloroform!" he gasped. "In some way Tom has been overcome by chloroform. I've got to get him to the fresh air."

Once he had solved the puzzle of Tom's unconsciousness, Ned was quick to act. He caught Tom under the arms, and dragged him out of the booth, and to the outer door of the shop. Almost before Ned had reached there with his limp burden, Tom began to revive, and soon the fresh, cool night air completed the work.

"I--I," began the young inventor. "Ned, I--I--"

"Now take it easy, Tom," advised his chum. "You'll be all right in a few minutes. What happened? Shall I call your father, or Koku?"

"No--don't. It would only--only alarm dad," faltered Tom. "I'm getting all right now. But he--he nearly had me, Ned!"

"He had you? What do you mean, Tom? Who had you?"

"I don't know who it was, but when I was talking to you over the wire, all of a sudden I felt a hand behind me. It slipped over my mouth and nose, and I smelled chloroform. I knew right away something was wrong, and I called to you. That's all I remember. I guess I must have gone off."

"You did," spoke Ned. "You were unconscious when I got to you. I couldn't imagine what had happened. First I thought it was an electrical shock. Then I smelled that chloroform. But who could it have been, Tom?"

"Give it up, Ned! I haven't the slightest idea."

"Could they have been going to rob you?"

"I haven't a thing but a nickel watch on me," went on Tom. "I left all my cash in the house. If it was robbery, it wasn't me, personally, they were after."

"What then? Some of your inventions?"

"That's my idea now, Ned. You remember some years ago Jake Burke and his gang held me up and took one of dad's patents away from me?"

"Yes, I've heard you mention that. It was when you first got your motor cycle; wasn't it?"

"That's right. Well, what I was going to say was that they used chloroform on me then, and--"

"You think this is the same crowd? Why, I thought they were captured."

"No, they got away, but I haven't heard anything of them in years. Now it may be they have come back for revenge, for you know we got back the stolen property."

"That's right. Say, Tom, it might be so. What are you going to do about it?"

"I hardly know. If it was Jake Burke, alias Happy Harry, and his crowd, including Appleson, Morse and Featherton, they're a bad lot. I wouldn't want father to know they were around, for he'd be sure to worry himself sick. He never really got over the time they attacked me, and got the patent away. Dad sure thought he was ruined then."

"Now if I tell him I was chloroformed again to-night, and that I think it was Burke and his crowd, he'd be sure to get ill over it. So I'm just going to keep mum."

"Well, perhaps it's the best plan. But you ought to do something."

"Oh, I will, Ned, don't worry about that. I feel much better now."

"How did it happen?" asked Ned, his curiosity not yet satisfied.

"I don't know, exactly. I was in the booth, talking to you, and not paying much attention to anything else. I was adjusting and readjusting the current, trying to get that image to appear on the plate. All at once, I felt someone back of me, and, before I could turn, that hand, with the chloroform sponge, was over my mouth and nose. I struggled, and called out, but it wasn't much use."

"But they didn't do anything else--they didn't take anything; did they, Tom?"

"I don't know, Ned. We'll have to look around. They must have sneaked into the shop. I left the door open, you see. It would have been easy enough."

"How many were there?"

"I couldn't tell. I only felt one fellow at me; but he may have had others with him."

"What particular invention were they after, Tom?"

"I'm sure I don't know. There are several models in here that would be valuable. I know one thing, though, they couldn't have been after my photo telephone," and Tom laughed grimly.

"Why not?" Ned wanted to know.

"Because it's a failure--that's what! It's a dead, sure failure, Ned, and I'm going to give it up!" and Tom spoke bitterly.

"Oh, don't say that!" urged his chum. "You may be right on the verge of perfecting it, Tom. Didn't you see any image at all on the plate?"

"Not a shadow. I must be on the wrong track. Well, never mind about that now. I'm going to look around, and see if those fellows took anything."

Tom was feeling more like himself again, the effects of the chloroform having passed away. He had breathed the fumes of it for only a little while, so no harm had been done. He and Ned made an examination of the shop, but found nothing missing.

There were no traces of the intruders, however, though the two chums looked carefully about outside the building.

"You were too quick for them, Ned," said Tom. "You came as soon as I called. They heard me speaking, and must have known that I had given the alarm."

"Yes, I didn't lose any time," admitted Ned, "but I didn't see a sign of anyone as I ran up."

"They must have been pretty quick at getting away. Well, now to decide what's best to do to-night."

After some consultation and consideration it was decided to set the burglar alarms in every building of the Swift plant. Some time previous, when he had been working on a number of valuable inventions, unscrupulous men had tried to steal his ideas and models. To prevent this Tom had arranged a system of burglar alarms, and had also fitted up a wizard camera that would take moving pictures of anyone coming within its focus. The camera could be set to work at night, in connection with the burglar alarms.

The apparatus was effective, and thus an end was put to the efforts of the criminals. But now it seemed Tom would have to take new precautionary measures. His camera, however, was not available, as he had loaned it to a scientific society for exhibition.

"But we'll attach the burglar wires," decided Tom, "and see what happens."

"It might be a good plan to have Koku on guard," said Tom's chum. "That giant could handle four or five of the chaps as easily as you and I could tackle one."

"That's right," agreed Tom. "I'll put him on guard. Whew! That chloroform is giving me a headache. Guess I'll go to bed. I wish you'd stay over to-night, Ned, if you haven't anything else to do. I may need you."

"Then of course I'll stay, Tom. I'll telephone home that I won't be in."

A little later Tom had put away his new photo telephone apparatus, and had prepared for the warm reception of any unbidden callers.

"I wish I hadn't started on this new invention," said Tom, half bitterly, as he locked up the main parts of his machine, "I know it will never work."

"Oh, yes it will," spoke Ned, cheerfully. "You never failed yet, Tom Swift, in anything you undertook, and you're not going to now."

"Well, that's good of you to say, Ned, but I think you're wrong this time. But I'm not going to think any more about it to-night, anyhow. Now to find Koku and put him on watch."

The giant listened carefully to Tom's simple instructions.

"If any bad men come in the night, Koku," said the young inventor, "you catch them!"

"Yes, master, me catch!" said Koku, grimly. "Me catch!" and he stretched out his powerful arms, and clenched his big hands in a way that boded no good to evildoers.

Nothing was said to Mr. Swift, to Mrs. Baggert, or to Eradicate about what had happened, for Tom did not want to worry them. The burglar alarms were set, Koku took his place where he could watch the signals, and at the same time be ready to rush out, for, somehow, Tom had an idea that the men who had attacked him would come back.

Tom and Ned occupied adjoining rooms, and soon were ready for bed. But, somehow, Tom could not sleep. He lay awake, tossing from side to side, and, in spite of his resolution not to think about his photo telephone invention, his mind ran on nothing but that.

"I can't see what next to do to make it work," he told himself, over and over again. "Something is wrong--but what?"

At length he fell into a fitful doze, and he had a wild dream that he was sliding down hill on a big mirror in which all sorts of reflections were seen--reflections that he could not get to show in the selenium plates.

Then Tom felt the mirror bobbing up and down like a motor boat in a storm. He felt the vibration, and he heard a voice calling in his ear:

"Get up, Tom! Get up!"

"Yes! What is it?" he sleepily exclaimed,

"Hush!" was the caution he heard, and then he realized that his dream had been caused by Ned shaking him.

"Well?" whispered Tom, in tense tones.

"Midnight visitors!" answered his chum "The burglar alarm has just gone off! The airship hangar drop fell. Koku has gone out. Come on!"