"That they have been killed?" Frank finished for him. "No, I do
not. Unless they fell in the fight and then we should have seen
their bodies down with the others by the river. No, it is my idea
that they have been carried off to be sold as slaves. They would
have a high market value you know."

Harry groaned.

"But don't you think there is a chance of our getting them back?"

Frank's face grew grave.

"Of course we are going to try every means in our power, but once in
the hands of that scoundrel Muley-Hassan it is doubtful if we ever
see them again. There is only one thing for us to do."

"And that is--?"

"To get back to the Moon Mountains at once. But we have no
gasoline."

This was a stunning blow; in the excitement their of fuel had not
occurred even to the farseeing Frank. They had had, as our readers
know, to leave most of their gasoline at the Moon Mountains in order
to lighten the aeroplane. Without it they could not move an inch in
their air-craft. Harry tested the tank. Only a few paltry gallons
remained--not enough to drive the aeroplane ten miles.

As the boys stood, struck dumb by the realization of the disaster