It was a week later, and the launch having towed the expedition as far up the river as Frank decided was necessary—before they struck out into the unknown land of the cannibals, winged men, and the ivory hoard—had returned to civilization several days before, carrying with it letters from all the adventurers which they felt might be the last they would write for some time. The spot selected for the permanent camp was a sort of park-like space covered at its edges with masses of manioc and banana bushes. Beyond towered huge tropical trees and beyond these again the blue outlines of the distant Moon Mountains in which, according to old Barr's map, lay the ivory cache.
It had been a busy week. The Golden Eagle II had been re-erected and her own wireless and the field wireless apparatus put in order. As our readers who have followed this series are familiar with the manner of setting up the great Chester aeroplane and her fittings, it would be tedious to repeat the description of the process. Suffice it to say that thanks to the clever simplicity of the "knock-down" arrangement, by which the ship could be taken apart and set up again, the operation of equipping her for active work was a comparatively light one. The extra gasoline and supplies for the camp in general were stored in a separate tent removed from the circle in which the boys' tents and those of Ben Stubbs and Professor Wiseman were pitched.
There was, too, a newcomer in the camp—a Portuguese named Diego de Barros. He was not a particularly well-favored individual, but he bore the reputation of having great power over the natives and of being very friendly to the white traders who penetrated into the interior. Once or twice there had been ugly talk about his being in league with the Arab slave and ivory traders, but he had managed to clear his name and along the Ivory Coast enjoyed the reputation of being an honest, reliable man. He had joined the boys' camp a few days before and his manner of coming was this.
While everybody was busy getting things in shape there had come a loud hail from the quarters of the native helpers, just outside the white man's encampment, announcing that a canoe was coming up the river. All hands had hastened to the river bank to find de Barros just putting his foot ashore from the canoe in which two natives had paddled him from the coast. He had with him some bales of cotton goods and a few gewgaws of various kinds and was bound, so he said, on a trading expedition into the back country. Further down the river he had heard, he explained, that the boys were camped where he found them, and he had determined to pay them a visit. The brief stay that the boys had interpreted this as meaning, however, had extended itself into three days and still Diego showed no inclination to leave.
"If he doesn't move on soon I shall be compelled to ask him to go," said Frank in an annoyed tone to Harry. "I don't want to be inhospitable, but we can't afford to have strangers hanging round the camp, there is too much at stake."
Harry agreed with him and the two boys decided to tell the Portuguese that evening as tactfully as possible that they were on a private enterprise and could not accommodate strangers. This decision arrived at, Frank turned to the steel strong box that was never out of his sight and drew from it the precious map of the Moon Mountains. Seated at the little camp-table—(the conversation just related had taken place in the Boy Aviators' tent)—the two pored over the document for hours. With dividers, compass and parallel rulers Frank, who was a skilled navigator, laid out an aerial course that would bring them, he calculated, unerringly to the spot marked by a red cross where—so old Luther Barr declared—lay the ivory that was to save Mr. Beasley from financial ruin and disgrace.
Frank laid his finger on the spot and exclaimed enthusiastically:
"There it is, Harry, and we are not so far from it now. In a few days we shall know whether we are on a wild-goose chase or not."
"Why, no doubt has ever entered your head that the ivory is there?" questioned Harry.
"Well, old fellow, you know there are others interested in this ivory beside ourselves—Muley-Hassan for instance."
"You think he had got ahead of us?"
"I did not say I thought so, I only say that it is possible that he may have done so."
"How could he have got wind of our coming?"
"In Africa there is a sort of underground wire for news," replied Frank. "I have no doubt that hundreds of natives far in the interior are by this time apprised of our coming."
Harry looked alarmed.
"That's bad," he said.
"Well, it couldn't be helped: but we may have other enemies nearer at hand."
"What do you mean?"
"That I don't like the looks of that Portuguese fellow. If he got wind of what we are doing he would be likely to ruin the whole object of our expedition."
"That's so. We'll have to get rid of him."
"Well, we are going to, and if he won't go for gentle means we'll try rough ones."
"Hullo, what's that?" exclaimed Harry suddenly.
The flap at the end of the tent toward which both of their backs had been turned had been suddenly drawn aside and in one quick, backward glance Harry made out the smiling figure of de Barros standing in the doorway. It might have been fancy, but he thought for a minute that the Portuguese had a peculiarly villainous expression on his dark, handsome features.
"Ah, senors," he said, as Frank, with a quick movement swept the map off the table—but not before de Barros's quick eyes had spied it. Fearing to replace the precious chart in the strong box, while the Portuguese lingered, Frank tucked it into his pocket.
"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.
"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 the smiling Portuguese.
"I just have to trouble you for that map I saw you put in your pocket, that is all," went on his captor, while the two huge negroes who had made Frank prisoner stood to one side immovable as carved figures.
"It is lucky for me that you came down to the river bank," grinned the Portuguese as he ran his hand over Frank's clothes, to ascertain the hiding-place of the precious map of the ivory cache, "otherwise I should have had to delay my departure till to-night, and possibly have cut your throat while you slept."
Frank felt as if his heart would burst with rage and mortification as the greasy, smiling Portuguese deliberately drew out the priceless document and gazed at it in triumph. He laid it on the ground beside him while lie resumed his search for other clues.
"That ivory belongs to my master—Muley-Hassan—now," he sneered; "did you think for a minute that we would ever let you white fools get it back again."
It was well for the Portuguese that Frank's hands were not free then. Had they been the dark-skinned traitor would have had a fight on his hands in a few seconds. But suddenly events took a strange turn.
The two blacks uttered a sharp cry of warning as the bushes parted and a huge form dashed out, whirling about its head a glistening axe.
It was Sikaso!
The next minute would have been Diego's last but that his two followers lifted him to his feet and, picking him up like a child, ran for his canoe with him. With a few rapid strokes they were in midstream and paddling up the river with powerful strokes while Sikaso raged impotently on the shore.
"Oh for one of the white men's fire-tubes!" he sighed, and even as he spoke a sharp reminder of the efficiency of these same "fire-tubes" whizzed past his ear in the shape of a bullet from Diego's revolver.
In a few steps the old black was beside his young leader and with a couple of strokes of his keen blade had set him free.
"Quick, Sikaso; the canoes—we must pursue him. Call the boys and Ben while I cast off the canoes. Quick, we have not a minute to lose."
Although Diego in his hurry had not carried off the map but left it lying on the ground, still Frank realized that the Portuguese had not actually needed the document to aid Muley-Hassan to find the cache. The Arab was no doubt familiar with the location anyway, but to head off all danger of the boys getting there first, it was vital to stop Diego at all costs. In a few bounds Frank reached the little indentation in the bank where the canoes were kept.
As he gained it he fell back with a groan and, brave boy as he was, he leaned weakly against a tree for support as the true extent of the crushing disaster that had occurred was borne in on him.
The canoes were gone!
The cunning rascal, Diego, had devised his plan well.
The painters of all the craft had been cut, and by this time they were doubtless miles down the stream.
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