,
Jack and Hal had the piston replaced and all the other parts in place
within fifteen minutes. Then, once more, Hal turned on the gasoline, set
the ignition, and watched.

The engine ran as smoothly as ever.

"There won't be any more trouble, unless someone is turned loose here with
files and a blast lamp," pronounced Hal. Then he and his chum sought the
deck, to report to the officer in charge.

"You think we're in running order, now?" asked that officer.

"If you give the speed-ahead signal, sir, I think you'll feel as though
you had a live engine under your deck," Hal assured him.

The signal was given, the "Pollard" immediately responding. She cut a wide
circle, at good speed, returning to her former position, where the
propellers were stopped.

"You suspect your own machinist, who was aboard?" asked the naval officer,
in a low tone, of the submarine boys.

"If you'll pardon our not answering directly, sir," Captain Jack replied,
"we want to have more than suspicions before we make a very energetic
report on this strange accident. But we shall not be asleep, sir, in the
matter of finding out. Then we shall make a full report to Mr. Mayhew."

"Success to you--and vigilance!" muttered the naval officer.

The gunboat's cutter came alongside, transferring Jack and Hal back to the
"Farnum."

Hal went directly below to the engine room.

"You fixed the trouble with the 'Pollard'?" demanded Eph Somers, eagerly.

"Yes," Hal admitted.

"What was wrong?"

"Why, I don't know as I'd want to commit myself in too offhand a way,"
replied Hal, slowly, as though thinking.

"What appeared to be at the bottom of the trouble?"

"Why, it _may_ have been that one of the naval machinists, not
understanding our engines any too well, allowed one of the pistons to get
overheated, and then resorted to filing," Hal replied.

"What? Overheat a piston, and then try to correct it with a file?" cried
young Somers, disgustedly. "The crazy blacksmith! He ought to be set to
shoeing snails--that's all he's fit for."

"It looks that way," Hal assented, smiling.

Artful, clever Hal! He had carried it all off so coolly and naturally that
Sam Truax, who had been closely studying Hastings's face from the
background, was wholly deceived.

"This fellow, Hastings, isn't as smart as I had thought him," muttered
Truax, to himself.

The interrupted cruise now proceeded, the parent vessel signaling for a
temporary speed of sixteen knots