o one
of Tom's employees had put it there, and it could not have fallen by
accident, for the motor connections were protected by a mesh of wire,
and a hand would have to be thrust under them to put the bar in place.
Tom gave a quick look at his men. He knew he could trust them--every
one. But this was a queer happening.

For a moment Tom did not know what to think, and then, as the memory of
that warning telegram came to him, he had an idea.

"Were any strangers in this cabin before the start was made?" he asked
Mr. Mound.

"Not that I know of," was the answer.

"Well, there may be some here now," Tom said grimly. "Look about."

But a careful search revealed no one. Yet the young inventor was sure
the bar of copper, which had done the mischief of short-circuiting the
motor, had been put in place deliberately.

In reality there was no danger to the craft, since there was power
enough in the storage battery to run it for several hours. But the
happening showed Tom he had still to reckon with his enemies.

He looked at the height gauge on the wall of the motor-room, and noted
that the Mars was going up. In accordance with Tom's instructions they
were sending her above the storm area. Once there, with no gale to
fight, they could easily beat their way back to a point above Shopton,
and make the best descent possible.

And that was done while, under Tom's direction, his men took the
damaged motor apart, with a view to repairing it.

"What was it, Tom?" asked Ned, coming back to join his chum, after
George Ventor, the assistant pilot, had taken charge of the wheel.

"I don't exactly know, Ned," was the answer. "But I feel certain that
some of my enemies came aboard here and worked this mischief."

"Your enemies came aboard?"

"Yes, and they must be here now. The placing of that copper bar proves
it."

"Then let's make a search and find them, Tom. It must be some of those
foreign spies."

"Just what I think."

But a more careful search of the craft than the one Tom had casually
made revealed the presence of no one. All the crew and helpers were
accounted for, and, as they had been in Tom's service for some time,
they were beyond suspicion. Yet the fact remained that a seemingly
human agency had acted to put the main motor out of commission. Tom
could not understand it.

"Well, it sure is queer," observed Ned, as the search came to nothing.

"It's worse than queer," declared Tom, "it's alarming! I don't k