ly captors so that it would be
impossible for him to move it without attracting their attention.

CHAPTER XXI.

OFF ON A SEA TRAIL.

As minutes and then hours elapsed and Rob did not return, Merritt became
first anxious, and then seriously alarmed. He knew Rob's daring nature,
and had a keen fear that it might have led him into doing something
reckless.

It was almost dawn when he at length determined to return to the
encampment and seek out Ensign Hargreaves. By the time he had tramped
back over the sandy dunes day was breaking, and in the camp of the Boy
Scouts the notes of the morning bugle were ringing out cheerily. The
first of the Scouts to note Merritt's return was Donald Grant.

He came running toward him, and then stopped short as he noted the
other's drawn, tired face.

"Why, what in the world's the matter with you, Merry?" he gasped out.
"You look as if you'd been drawn through a knothole. Where's Rob? Where
have you been all night?"

"I'll explain that later," said Merritt wearily; "just now I've got to
find Ensign Hargreaves. Rob's either been kidnapped or lost."

He hastened on, leaving the other lad rooted to the spot with amazement
and alarm. He knew Merritt well enough already to realize that the other
was not the sort of lad to overrate a situation. If Merritt was as
scared and weary as he looked, something serious indeed must have taken
place.

In the meantime Merritt hastened to Ensign Hargreaves' tent. Hastily
arousing him, he hurriedly explained the whole matter. The officer was
out of his cot in an instant.

"You had no business to go off alone like that without notifying me,"
he exclaimed rather sharply. "Don't you know that the first duty of a
soldier, a sailor or a scout is to obey orders?"

Merritt crimsoned and hung his head. He knew that the officer was right.

"We thought we were doing a good thing," he said, "but I know now that
we did wrong in not notifying you."

The ensign's hand fell on the lad's shoulder. Then kindly enough he
said:

"Well, acknowledging that you did wrong is a manly thing, my boy, and
we'll say no more about the matter. But about Rob, something must be
done right away. Arouse Mr. Barr while I am dressing and we'll set about
searching for him at once. There's little doubt in my mind but that he
is on that island where you saw the signals flying."

"But how could he get there unless he had an airship?" inquired Merritt.

"Hasn't it occurred