Jack pursued, but could find no one, and the sound of moving feet had also ceased.  As soon as he was satisfied that he could not catch the prowler, the submarine boy returned to the room.

“Do you see this?” asked the shipbuilder, holding out the slip of paper.

“Another warning, I suppose?” Benson ventured.

“Yes; and it shows that you are being followed and watched.  Something worse is almost certain yet to happen.”

Jack took the slip of paper, reading these printed words: 

“You have been fairly warned.  Are you going to be a fool?  Obey, or—­”

That was all.  The meaning of the words was plain enough, but Jack, with as cool a smile as ever, folded the slip, dropping it in one of his pockets.

“This will interest Trotter,” he remarked.

“There is no use whatever in advising you, suppose?” asked the shipbuilder.

“If these threats were directed against you, would you cringe from them?” demanded the young submarine captain.

“Of course I wouldn’t,” replied Farnum, a sudden flash lighting his eyes as he spoke.

“Then why should you expect to see me turn coward?”

“I won’t say another word about it, Jack!” replied the shipbuilder, gripping his captain’s hand.  “I have dreaded to see you go down under the mysterious assaults of these scoundrels.  I have hated to see a boy come to that harm while serving me.  But I realize, now, that it would hurt you worse to run away than it would to stay and face any kind of punishment or even death itself.”

“That’s the talk, sir,” nodded Hal.  “And no one is going to harm him, either.  There are too many of us—­if we keep our eyes open.”

That “if” covered a wide field of possibilities.  Not one of them could foresee all that the ingenuity of the enemy would provide in the way of danger.

To quiet his own agitation Jacob Farnum had recourse to a cigar.  He lighted it, smoking with a very solemn look on his face.

“What’s all the excitement, I wonder?” muttered Hal, presently.

The distant sound of running feet, then cries came to their ears, though none in the little party could distinguish the words.

“There’s some big excitement on.  Come along,” urged Jack, reaching for his cap.

“Humph!  We’ve had excitement enough to last reasonable people for a long time,” grumbled the shipbuilder, but he, too, sprang for his hat.

Ere they had run far through the corridor they encountered other guests fleeing.

“What’s the matter?” called Jack.

“Fire in the south wing,” called back one man.  “We don’t know, yet, whether the hotel is doomed.”

Just then the fire alarm bell of the hotel began to sound loudly in all the corridors.

That brought the remaining guests on the run, some appearing not completely dressed.

As the rushing throng began to thicken at a door on the ground floor the sound of a whistled of clanging gongs was heard without.  The Spruce Beach fire department was responding to the alarm.