At last, after disconnecting some parts, Hal drew out a long, slender
brass piston.

As he held it up young Hastings's face went as white as chalk.

"Do you see this?" he demanded, hoarsely.

"Filed, crazily, and it also looks as though the inner end had been
heated and tampered with," gasped Jack Benson.

"This, sir," complained Hal, turning around to face the naval officer
in charge, "looks like a direct attempt to tamper with and damage the
engine. Someone has done this deliberately, sir. It only remains to
find the culprit."

"Then we'll find out," retorted the naval officer, "if it takes a court
of inquiry and a court martial to do it. But are you sure of your
charge, Mr. Hastings?"

"Am I sure?" repeated Hal, all the soul of the young engineer swelling
to the surface. "Take this piston, sir, and examine it. Could such
a job have been done, unless by sheer design and intent?"

"Will the lieutenant permit me to speak?" asked the senior machinist,
taking a step forward and saluting.

"Yes; go ahead."

"Yesterday morning, sir," continued the senior machinist, "we thought
the engines needed some overhauling by someone more accustomed to them
than we were. We saw one of the machinists of the 'Farnum,' sir,
hanging about on shore. So we invited him aboard and asked him to look
the engines over."

"Describe the man," begged Jack.

The senior machinist gave a description that instantly denoted Sam Truax
as the man in question.

"Did you leave him alone in here, at any time?" demanded Hal.

"Let me see. Why, yes, sir. The man must have been alone in here some
three-quarters of an hour."

Jack and Hal exchanged swift glances.

There seemed, now, very little need of carrying the investigation
further.

CHAPTER XV

ANOTHER TURN AT HARD LUCK

When he could trust himself to speak Hal Hastings addressed the naval
officer.

"I think Mr. Benson and myself understand, sir, how it happened that
this damage was done. There are extra parts in the repair kit. In
twenty minutes, sir, I think we can have the engines running smoothly
once more."

The naval officer was wise enough not to press the questioning further
just then. Instead, he went on deck.

Working like beavers, and with the assistance of others standing about,
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