"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 know when I'll be safe if we have ghosts aboard."
"Ghosts?" repeated Ned.