Harry looked vexed.

"That's tough luck," he said. "If he overheard even a part of our
talk he must realize the object of our presence in Africa. And," he
went on, "I don't know a man on the Dark Continent whom I would
trust less than Diego de Barros, even the little we've seen of him."

"It can't be helped now," said Frank briefly; "come on, let's go and
put the finishing touches on the good old Eagle."

They worked the rest of the afternoon putting the big aeroplane in
shape for her flight to the Moon Mountains which it had been
determined to make the next day. It was almost dusk when Harry, who
was working over the engines, asked Frank for the reserve park-plug
box.

"It's in one of the canoes. I'll go and get it," said Frank, and at
once set off toward the river bank for that purpose. His path led
through a thick grove of bamboos which hid him from the view of the
camp after he had traversed a short distance. As he merged on the
river bank, whistling softly to himself, the young leader suddenly
felt himself pinioned by arms that seemed of enormous strength--
though, as the attack had come from behind, he could not see the
faces of his assailants. The next minute he was lying flat on his
back, bound and helpless with a bit of greasy cloth shoved in his
mouth for a gag.

"Keep still, senor, and you shall not be hurt;" said a quiet voice
near at hand, and Frank saw bending above him the sallow features of