"What's that? Your dye formulae here in my office?" cried Mr. Keith, for he had heard something of the chemist's loss, though he did not directly associate Field and Melling with it.

"That's what this is! The very papers, containing all the rare secrets, for which I have been so at a loss!" cried the delighted old man. "Now I can give to the world the dyes for which it has long been waiting! Oh, Tom Swift, you did more than you knew when you put out this fire!" and he hugged the bundle of smoke- smelling papers to his breast.

"But how did they get here?" asked the young inventor. "I know that Field and Melling had offices in this building. They were starting a new dye concern, and, though Mr. Baxter and I suspected them of having stolen his secret, we couldn't prove it."

"But we can now!" cried Mr. Baxter. "Though I don't know that I'll bother even to accuse them, as long as I have back my previous papers. I see how it happened. They had the formulae in their office. They rushed out with the documents, and, when they found they couldn't get past this floor, they went into Mr. Keith's office. There, in their excitement, they dropped the papers, and you put the fire out just in time, Tom, or they'd have been burned beyond hope of saving. You have given me back something almost as valuable as life, Tom Swift!"

"I'm glad I could render you that service," said the young inventor. "And I had no idea, when I dropped the chemicals, that I was saving someone even more valuable than your secret formulae," and they all knew he referred to Mary Nestor.

An examination of the papers found on Mr. Keith's office floor showed that not one of the dye secrets was missing. Thus Mr. Baxter came into possession of his own again, and when Field and Melling were sufficiently recovered they were charged with the theft of the papers. The charge was proved, and, in addition, other accusations were brought against them which insured their remainder in jail for a considerable period.

As Mr. Baxter had suspected, Field and Melling had, indeed, robbed him of his dye formulae papers. They learned that he possessed them, and they invited him to a night conference with the purpose of robbing him. The fire in their factory was an accident, of which they took advantage to make it appear that the chemist lost his papers in the blaze. But they had taken them, and though they did not mean to leave poor Baxter to his fate, that would have been the result of their selfish action had not Tom and Ned come to the rescue. And it was of this "putting over" that Field and Melling had boasted, the time Tom overheard their talk at Meadow Inn.

As Mr. Baxter guessed, the letter delivered to him at Tom's place was one that the two scoundrels would have retained, as they had others like it, if they had seen it. But a new clerk forwarded it, and the evidence it contained helped to convict Field and Melling.

As for the Landmark Building, while badly damaged, it would have been worse burned but for Tom's prompt action. And though he was more than glad that he had been on hand, he rather regretted that he could not give the test for which he had set out.

Eventually the building was made more nearly fire-proof and the fire-escapes were rebuilt, and Mr. Blake did not lose his money, as he had feared, though Barton Keith said it was more owing to Tom Swift's good luck than to Mr. Blake's management.

But, as it developed, nothing could have been more opportune than Tom's action, for word of his quenching a bigger blaze than he would have had to encounter in the official test reached the Denton fire department. As a result there was a conference, and, after only a nominal showing of his apparatus, it was adopted by a unanimous vote.

But this occurred some time afterward, for, following his rescue of Mary Nestor and her uncle and the saving of the lives of Field and Melling, as well as others in the building, by his prompt smothering of the fire, Tom returned to Shopton.

He and his companions went in the Lucifer, minus, now, the big load of chemicals, and on landing near the hangar Tom was surprised to see Koku the giant running toward him. The big man showed every symptom of great excitement as he cried:

"Oh, Master Tom! He see the light ob day! he see the light ob day now! Oh, so glad! So glad!"

"Who sees the light of day?" asked the young inventor.

"Black Rad! Eradicate! Him eyes all better now! Pill man take off cloth. Rad--he see light ob day!"

"Oh, I'm so glad! So thankful!" cried Tom. "How I've wished for this! Is it really true, Koku?"

"Sure true! Pill man say Rad see K O now." The giant, doubtless, meant "O K," but Tom understood. And it was true, as he learned more directly a little later.

When Tom entered the room where Rad had been kept in the dark ever since the explosion, the colored man looked at his master with seeing eyes, though the apartment was still but dimly lighted.

"I's all right ag'in now, Massa Tom!" cried Rad. "See fine! I's all ready to make more smellin' stuff to put out fires!"

"You won't have to, Rad!" cried Tom joyfully. "My chemical extinguisher is completed, and you did your share in making it a success. But I never would have felt like claiming credit for it if you had been--had been left in the dark."

"No mo' dark, Massa Tom!" said Eradicate. "I kin see now as good as eber, an' yo'-all won't hab to 'pend on dat lazy good- fo'-nuffin cocoanut!" and he chuckled as he looked at the giant.

"Huh! Lazy!" retorted the big man. "I show you--black coon!"

"By golly!" laughed Rad. "Him an' me good friends now, Massa Tom. Neber I fuss wif Koku any mo'! He suah was good to me when I had to stay in de dark!"

Of course it would be too much to hope that Koku and Eradicate never again quarreled, but for a long time their warm friendship was a thing at which to marvel, considering the past.

"Well, I guess this settles it," said Tom to Ned one day, after going over the day's mail.

"Settles what, Tom?"

"My aerial fire-fighting apparatus. Here's word from the National Fire Underwriters Association that they have adopted it, and there will be a big reduction of rates in all cities where it is a part of the fire department equipment. It's been as great a success as Mr. Baxter's new dye."

"Yes, and he has had wonderful success with that. But what are you going to do now, Tom? What new line of endeavor are you going to aim at?"

Tom arose and reached for his hat.

"I am now going," he said, with a grin, "to see somebody on private business."

"You are going to see Mary Nestor!" broke out Ned.

"I am," said Tom.

And he did.