“He knew the fire would be practically unquenchable by ordinary means, and he counted on its soon eating its way into the carbide and other explosives.  Only it didn’t.”

“Why, Tom!” cried Ned.  “It was just like one of those alarm-clock dynamite bombs—­set to go off at a certain time.”

“Exactly,” Tom said, “only this was more delicate, and, if it had worked properly, there wouldn’t have been a vestige left to give us a clue.  But the fire, thanks to the ballast sand in the dirigible, was put out in time.  The fuse burned itself out, but I can tell by the smell that chemicals were in it.  That’s all, Koku,” he went on to the giant who had stood waiting, not understanding all the talk between Tom and Ned.  “I’ll take care of this now.”

“Bad man put it there?” asked the giant, who at least comprehended that something was wrong.

“Well, yes, I guess you could say it was a bad man,” replied Tom.

“Ha!  If Koku find bad man—­bad for that man!” muttered the giant, as he clasped his two enormous hands together, as though they were already on the fellow who had tried to do Tom Swift such an injury.

“I wouldn’t like to be that man, if Koku catches him,” observed Ned.  “Have you any idea who it could be, Tom?”

“Not the least.  Of course I know I have enemies, Ned.  Every successful inventor has persons who imagine he has stolen their ideas, whether he has ever seen them or not.  It may have been one of those persons, or some half-mad crank, who was jealous.  It would be impossible to say, Ned.”

“It wouldn’t be Andy Foger, would it?”

“No; I don’t believe Andy has been in this neighborhood for some time.  The last lesson we gave him sickened him, I guess.”

“How about those diamond-makers, whose secret you discovered?  They wouldn’t be trying to get back at you, would they?”

“Well, it’s possible, Ned.  But I don’t imagine so.  They seem to have been pretty well broken up.  No, I don’t believe it was the diamond-makers who put this fire bomb in the red shed.  Their line of activities didn’t include this branch.  It takes a chemist to know just how to blend the things contained in the bomb, and even a good chemist is likely to fail—­as this one did, as far as time went.”

“What are you going to do about it?” Ned asked.

“I don’t know,” and Tom spoke slowly, “I hoped I was done with all that sort of thing,” he went on; “fighting enemies whom I have never knowingly injured.  But it seems they are still after me.  Well, Ned, this gives us something to do, at all events.”

“You mean trying to find out who these fellows are?”

“Yes; that is, if you are willing to help.”

“Well, I guess I am!” cried the bank clerk with sparkling eyes.  “I wouldn’t ask anything better.  We’ve been in things like this before, Tom, and we’ll go in again—­and win!  I’ll help you all I can.  Now, let’s see if we can pick up any other clues.  This is like old times!” and Ned laughed, for he, like Tom, enjoyed a good “fight,” and one in which the odds were against them.