"Ah, senors, good afternoon," grinned the unwelcome visitor. "I have come to say 'adios.' I am going up the river to-night and may not see you again for a long time."
"I am sorry to have you leave," said Frank with a heartfelt wish that de Barros would hasten his departure.
"I knew you would be," smiled the Portuguese, "but it is the lot of man to meet and part. Adios, senors, I go to make ready."
He vanished as suddenly as he had come upon the scene.
"What do you make of that?" inquired Harry.
"I don't know what to think. I have an idea that he was listening to every word of our conversation just now and that he saw the map before I had time to sweep it off the table."
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.