returned his hawk-like gaze unflinchingly.

"No, sir," spoke up Diego, "they are not. Wiseman has just told me
that the Chester boys have flown in their air-ship and these are the
cubs left behind to guard the camp."

At Wiseman's name mentioned in such a connection both the boys
started.

"What! they have gone?" thundered the Arab chief.

"Yes, sir," stammered Diego, his coward nature aroused at the sight
of his superior's fury.

"And by this time they are rifling the ivory cache. That fool
Wiseman shall pay dearly for this. Bring him to me," shouted the
Arab.

Desperate as was the boys' position they could not restrain a start
of amazement as Professor Wiseman, his face pale as ashes to his
very lips, came tremblingly forward.

"You were attached to this boys' camp to prevent by all means their
sailing till I attacked the camp and made them prisoners, were you
not?" demanded Muley-Hassan angrily.

Wiseman stammered something in reply.

"You are a coward as well as a fool," went on the slave-dealer, a
cruel sneer breaking over his face; "but you have blundered for the