"What's that?" exclaimed Mary Nestor, giving such a start as she sat opposite Tom at the restaurant table that she dropped the bill of fare she had been looking over.

A crash had resounded through the room, but it spoke well for the state of Tom's nerves that he gave no indication that he had heard the noise. It was caused by a waiter when he dropped a plate, which was smashed into pieces on the floor. The noise was startling enough to excuse Mary for jumping in her chair, and it seemed to put an end to the strange talk of "Mr. High" and "Mr. Low" back of the screen, for after the crash of china only indistinct murmurs came from there. But Tom Swift did not cease to wonder at the import of the talk about chemicals, fire, and the mention of the name of Josephus Baxter.

"I think I'll try some of those Murolloas, as they call them, Tom," announced Mary, having made her selection of the pastry. "And may I have another cup of tea?"

"Two if you like," answered the young inventor. "They say tea is good for the nerves, and you seem to need something, judging by the way you jumped when that plate fell."

"Oh, Tom, that isn't fair! After the way we had to come down in your 'plane!" objected Mary.

"That's right!" he conceded. "I forgot about that. My fault, entirely!"

Mary smiled, and seemed to have regained her composure. Tom glanced at her anxiously, not because of what he thought might be the state of her nerves, but to see if she had sensed anything the two men behind the screen had said. But the girl gave no indication that her mind had been occupied with anything more than the selection of her dessert.

"I wonder who they are, and what they meant by that talk," mused Tom, as the waiter served the Murolloas to him and Mary. "Poor Baxter! It looks as if he might have more enemies than the fireworks men he accuses of having taken his valuable formulae. I must see him soon, and have a talk with him. Yes, I must make a special point to see Josephus Baxter. But first I'd like to have a glimpse of these men.

Tom's wish in this respect was soon gratified, for before he and Mary had finished their pastry and tea there was a scraping of chairs back of the sheltering screen, and the two men, "Mr. Low" and "Mr. High," who had finished their meal, came forth.

Tom's judgment as to the statures of the men, based on the quality of their voices, was not exactly borne out. For it was the big man who had the high pitched, squeaky voice, and the little man who had the deep, rumbling tones.

They passed out, without more than a glance at Tom and his companion, but the young inventor peered at them sharply. As far as he could tell he had seen neither of them before, though he had an idea of their identity.

Tom took the chance to make certain this conjecture when Mary left her seat, announcing that she was going to the ladies' parlor to arrange her hair, which the run to escape from the rain had disarranged.

"Some storm," Tom observed to the waiter, who came up when the young inventor indicated that he wanted his check.

"Yes, sir, it came suddenly. Hope you didn't have to change a tire in it, sir."

"No, my machine isn't that kind," replied Tom, as he handed out a generous tip. "If I need a new tire I generally need a whole new outfit."

"Oh, then--" Obviously the man was puzzled.

"We came in an aeroplane," Tom explained. "But we had to make a forced landing. Is there a garage near here? I may need some help getting started."

"We accommodate a few cars in what was once the barn, and we have a good mechanic, sir. If you'd like to see him--"

"I would," interrupted Tom. "Tell the young lady to wait here for me. I'll see if I can get the Scud to work. If not, I'll have to telephone to town for a taxi. Did those men who just left come in a car?" and he nodded in the direction taken by the two who had dined behind the screen.

"Yes, sir. And they had engine trouble, I believe. Our man fixed up their machine."

"Then he's the chap I want to see," thought Tom. "I'll have a talk with him." He reasoned that he could get more about the identity of the two mysterious men from the mechanic than from the waiter. Nor was he wrong in this surmise.

"Oh, them two fellers!" exclaimed the mechanician, after he had agreed to go with Tom to where the airship Scud was stalled. "They come from over Shopton way. They own a fireworks factory-- or they did, before it burned."

"Are they Field and Melling?" asked Tom, trying not to let any excitement betray itself in his voice.

"That's the names they gave me," said the man. "Little man's Field. He gave me his card. I'm going to get a job overhauling his car. There isn't enough work here to keep a man busy, and I told 'em I could do a little on the outside. This place just started, and not many folks know about it yet."

"So I judge," Tom said. "Well, I'll be glad to have you give me a hand. I fancy the carburetor is out of order."

And this, when the young inventor and the mechanician from Meadow Inn reached the stranded Scud, was found to be the case. The storm had passed, and Mary told Tom she would not mind waiting at the Inn until he found whether or not he could get his air craft in working order.

"There you are! That's the trouble!" exclaimed the mechanician, as he took something out of the carburetor. "A bit of rubber washer choked the needle valve."

"Glad you found it," said Tom heartily. "Now I guess we can ride back."

While preparations were being made to test the Scud after the carburetor had been reassembled, Tom's mind was busy with many thoughts, and chief among them were suspicions concerning Field and Melling.

"If their talk meant anything at all," reasoned the young inventor, "it meant that there was some deal in which Josephus Baxter got the worst of it. 'Putting it over on him in the fire,' could only mean that. Of course it isn't any of my business, in a way, but I don't think it is right to stand by and see a fellow inventor defrauded.

"Of course," mused Tom, while his helper put the finishing touches to the carburetor, "it may have been a business deal in which one took as many chances as the other. There are always two sides to every story. Baxter says they took his formulae, but he may have taken something from them to make it even. The only thing is that I'd trust Baxter sooner than I would those two fellows, and he certainly had a narrow squeak at the fire.

"But I have my own troubles, I guess, trying to perfect that fire-fighting chemical, and I haven't much time to bother with Field and Melling, unless they come my way."

"There, I reckon she'll work," said the mechanician, as he fastened the last valve in the carburetor. "It was an easier job than I expected. Wasn't as much trouble as I had over their car those two fellers you were speaking of--Field and Melling. They're rich guys!"

"Yes?" replied Tom, questioningly.

"Sure! They've started a big dye company."

"A dye company?" repeated the young inventor, all his suspicions coming back as he recalled that Baxter had said his formulae were more valuable for dyes than for fireworks.

"Yes, they're trying to get the business that used to go to the Germans before the war," went on the man.

"Yes, the Germans used to have a monopoly of the dye industry," said Tom, hoping the man would talk on. He need not have worried. He was of the talkative type.

"Well, if these fellers have their way they'll make a million in dyes," proceeded the mechanician, as he stepped down out of the airship. "They've built a big plant, and they have offices in the Landmark Building."

"Where's that?" asked Tom.

"Over in Newmarket," the man went on, naming the nearest large city to Shopton. "The Landmark Building is a regular New York skyscraper. Haven't you seen it?"

"No," Tom answered, "I haven't. Been too busy, I guess. So Field and Melling have their offices there?"

"Yes, and a big plant on the outskirts for making dyes. They half offered me a job at the factory, but I thought I'd try this out first; I like it here."

"It is a nice place," agreed Tom. "Well, now let's see if she'll work," and he nodded at the Scud.

It needed but a short test to demonstrate this and soon Tom went back to the Inn for Mary.

"Are you sure we shall not have to make an. other forced landing?" she asked with a smile, a she took her place in the cockpit.

"You can't guarantee anything about an aeroplane," said Tom. "But everything is in our favor, and if we do have to come down I have a better landing field than this." He glanced over the meadow near the wayside inn.

"I suppose I'll have to take a chance," said Mary.

However, neither of them need have worried, for the Scud tried, evidently, to redeem herself, and flew back to Shopton without a hitch. After making sure that his engine was running smoothly, Tom found his mind more at ease, and again he caught himself casting about to find some basis for his suspicious thoughts regarding the two men who had talked behind the screen.

"What is their game?" Tom found himself asking himself over and over again. "What did they 'put over' on poor Baxter?"

Tom had a chance to find out more about this, or at least start on the trail sooner than he expected. For when he landed he saw Koku, the giant, coming toward him with an appearance of excitement.

"Is Rad worse? Is there more trouble with his eyes?" asked the young inventor.

"No, him not much too bad," answered Koku. "I keep him good as I can. He sleep now, so I come out to swallow some fresh air. But man come to see you--much mad man."

"Mad?" queried Tom.

"Well, what you say--angry," went on Koku. "Man what was in Roman Skycracker blaze."

"Oh, you mean Mr. Baxter, who was in the fireworks blaze," translated Tom. "Where is he, and what's the matter?"