inventor had passed out, reviewing in his mind the talk just finished.

"I wonder," said Tom slowly, "if any of the new men could have obtained
work here for the purpose of furthering that plot the lieutenant
suspects? I wonder if that could be true?"

And the more Tom thought of it, the more he was convinced that such a
thing was at least possible.

"I must make a close inspection, and weed out any suspicious
characters," he decided, "though I need every man I have working now,
to get the Mars finished in time. Yes, I must look into this."

Tom had reached a point in his work where he could leave much to his
helpers. He had several good foremen, and, with his father to take
general supervision over more important details, the young inventor had
more time to himself. Of course he did not lay too many burdens on his
father's shoulders since Mr. Swift's health was not of the best.

But Tom's latest idea, the aerial warship, was so well on toward
completion that his presence was not needed in that shop more than two
or three times a day.

"When I'm not there I'll go about in the other shops, and sort of size
up the situation," he decided. "I may be able to get a line on some of
those plotters, if there are any here."

Lieutenant Marbury had departed for a time, to look after some personal
matters, but he was to return inside of a week, when it was hoped to
give the aerial warship its first real test in flight, and under some
of the conditions that it would meet with in actual warfare.

As Tom was about to leave his office, to put into effect his new
resolution to make a casual inspection of the other shops, he met Koku,
the giant, coming in. Koku's hands and face were black with oil and
machine filings.

"Well, what have you been doing?" Tom wanted to know. "Did you have an
accident?" For Koku had no knowledge of machinery, and could not even
be trusted to tighten up a simple nut by himself. But if some one
stood near him, and directed him how to apply his enormous strength,
Koku could do more than several machines.

"No accident, Master," he replied. "I help man lift that hammer-hammer
thing that pounds so. It get stuck!"

"What, the hammer of the drop forger?" cried Tom. "Was that out of
order again?"

"Him stuck," explained Koku simply.

There was an automatic trip-hammer in one of the shops, used for
pounding out drop forgings, and this hammer seemed to take especial
delight in getting out of order. Ve