The sun was just poking his rim above the western horizon and the chilly damp of early dawn lay over the island.  The sea, as calm almost as a lake, lay sullen and gray, scarcely heaving.  Behind the sleeping camp a few shreds of mist—­the ghosts of the vapors of the night were arising like smoke among the dim trees.  At the further end of the assemblage of tents, and beyond the smoldering fire, stood a silent figure, that of Ernest Thompson.

“Have you explored the island thoroughly?” asked Merritt under his breath.  Somehow the dim hour and the situation seemed to preclude the idea of loud talking.

“Of course not.  Not yet,” breathed the other in the same tones.  “We will break the news to the rest of the Patrol after breakfast.  It’s no use alarming them yet.”

“It isn’t possible that he went off on an early fishing expedition?”

For answer, Rob waved his hand toward the water, where the Flying Fish lay rocking gently at her anchor.  Ashore the dingy lay as Merritt and his companions had left it the night before.

“But what can have happened to him?” burst out Merritt, as they made their way over to Ernest Thompson’s side.

“I cannot think.  It is absolutely mystifying.  I am going to start for the captain’s place now.  He may be able to throw some light on the affair.”

Merritt shook his head.

“Hardly likely.  If there is no trace of Joe Digby on this side of the island, it is improbable that Captain Hudgins knows anything about him.”

“Well,” rejoined Rob in a troubled voice, “we’ve got to try everything.  I am responsible for his safe keeping while he is in camp.  I blame myself for allowing the kid to go on sentry duty at all.”

“No use doing that,” comforted Merritt; “there’s one thing sure, he can’t have melted away.  He must be somewhere on the island.  There are no wild beasts or anything like that here to carry him off, so if we keep up the search we must come upon him sooner or later.”

“That’s what makes the whole affair the more mystifying,” rejoined Rob.  “What can have become of him?”

“Well, if he’s on the island, we’ll find him,” he continued; “and if he isn’t—­”

“We’ll find him anyway,” declared Merritt in a determined voice.

“That’s the stuff!” warmly exclaimed the other.  “And now I’m going to take a cruise round to the other side of the island, and see if I can find out anything there.”

A few seconds later he was in the dinghy and sculling out over the water to the speedy Flying Fish.  In a short time he was off.

As the “chug chug” of the motor grew fainter, Merritt turned to young Thompson.

“Don’t breathe a word of this to the others till we know for certain that Digby has vanished,” he said.

The other boy nodded.

“I understand,” he said, and the look with which he accompanied the words rendered Merritt perfectly confident that he would be obeyed.