THERE was not a moment to lose. With the huge white condor swooping down upon them, the explorers knew that they must act quickly. Unfortunately their rifles had been left on the trail above. Before they could secure the weapons the huge bird would be upon them and would probably use its terrible claws and beak to great advantage.

“My knife is all we have to defend ourselves with,” said Joe, watching the large form advance toward them. “But I’m going to use it.”

The condor came on swiftly. It circled around a few times near its nest and then rushed madly at the little group of adventurers.

Now it was barely ten feet away and coming with deadly aim. In but a brief moment it would be in a position where it could work deadly havoc with its sharp claws.

Joe had his long hunting knife in readiness now, waiting for an opportune moment. Then it came.

The huge white bird was soaring directly above its human enemies. As it dropped lower, Joe lunged forward and plunged the sharp knife through one of the long, thin legs.

Uttering a curious sound, the condor darted away, circled around for a brief period, and then flew at the explorers with a new determination.

One of the horrible claws shot out and caught Joe’s arm, the impact knocking the knife from the youth’s hand. It went hurtling to the bottom of the abyss, far below.

Joe was weaponless, helpless!

New horror crept over him when he suddenly felt himself leaving the ground. Not fifteen feet away was the edge of the cliff! Vainly he tried to escape from the clutch of that formidable claw.

Meanwhile, Bob and the old man were not inactive. They knew that it would only be a short time before their friend would be carried over the brink of the cliff. And that must be prevented at any cost.

Looking wildly about, Bob caught sight of a rock about half as large as a brick. Almost frantic, he picked it up, and with desperate strength he sent it crashing into the condor’s body.

The force was terrific, and for a moment it seemed as if the condor were going to drop. But it righted itself and carried the helpless Joe still farther toward the rocky edge.

“I’m going to try something,” blurted out Bob, his face red with an awful fear. “You run up to the mules and get a rifle – quick!” he said to Dr. Rander.

As a last resort, Bob hurled his hundred and eighty pounds at Joe’s feet, and caught hold with a grip of steel. He wondered if the huge bird could lift both himself and his friend. If it could…

At that moment Dr. Rander scrambled down the rocky slope with a rifle, which he aimed unflinchingly at the condor’s body. The next moment the gun barked.

With a terrific fluttering of its heavy wings, the bird sank slowly to the ground. It touched the hard soil, and then with a convulsive twitch it lay still.

For almost a minute there was silence among the little party of adventurers. They were panting furiously, and their wide eyes had not yet lost their look of terror. Perspiration was streaming from them, making their faces shine gruesomely. It had been one of the narrowest escapes they had had so far.

Finally Joe wiped his face and looked at Bob with intense gratitude. Then his eyes fell on Dr. Rander, whose rifle was still warm from the timely shot.

“I don’t know how to thank you,” he said warmly. “If you hadn’t been so plucky, I would probably be lying in a broken mass at the bottom of the gorge right now. It was simply wonderful!”

“Forget it!” Bob disclaimed any praise offered him. “The only thing now that matters is that you’re alive.”

“Thank Bob for that,” the old man said. “If he had not thrown himself at your feet you would surely have gone over the cliff.”

“But it was your shot that finished the job,” protested Bob Holton. “Even with the weight of both of us the condor was slowly dragging us toward the brink.”

“I’m afraid my bullet would have been too late if you hadn’t done what you did,” persisted the old man.

“All right. Have it your own way.” With a laugh Bob dropped the matter and stooped over to examine the huge white bird.

It must have had a wing spread of over ten feet. Later measurements showed that this was accurate. But what impressed the youths most was its pure white feathers, which looked as clean as if they had been recently washed. The terrible claws and long sharp beak next caught the youths’ eyes, and their respect for the power of this monstrous bird was increased.

“Quite a specimen,” observed Joe. “And speaking of specimens,” he went on, “why can’t we skin it and take it with us? Our dads and Mr. Wallace would sure be tickled. The white condor! Boy! I can just see them giving cries of delight.”

“Nothing to prevent us,” returned the other youth. “We may find it hard to place in our mule train, but we’ll manage some way.”

Bob secured a long knife, and with a skill that he learned while on other hunting trips he cut the bird’s skin open down the breast. A few minutes more and the task was completed.

Without the weight of the body, the skin was light, and they had no difficulty in tying it over the back of one of the mules, which appeared not to notice the extra load.

With one last look at the spot where Joe had almost met his death, they turned and drove the pack animals ahead on the remainder of the journey to Pasaje.

But now they were more anxious than ever to reach their destination and fly with Karl Sutman to the place where their fathers were hunting. With every minute they longed still more to reach the town they were approaching.

“I hope nothing further comes up to stay us,” remarked Bob, as they descended a steep slope. “Somehow I’ve had enough excitement for a while.”

“So have I,” said Joe. “But of course there’s no way of telling what we may meet in these mountains.”

The next day they found themselves in a wide valley, which was covered with a heavy growth of dense vegetation. Tree ferns were quite prominent, growing in large clusters that dotted the valley. Bright flowers were also numerous, some of them unusual in shape and form.

And with this heavy vegetation came several varieties of wild animals, among them being foxes, lizards, guinea pigs, and a host of birds. The youths could easily have shot some, but they did not wish to lose time in doing so.

“I believe we are getting close to Pasaje now,” announced the old man, as he led the way around the winding Apurimac River.

Notwithstanding this, they traveled all that day without coming to the town. Camp was made at a clearing near the stream, supper was prepared, and then all retired, knowing that the following day would witness their coming to their destination.

Early the next morning the young men saw something that thrilled them with delight. They had been breaking camp and were almost ready to resume the tramp when suddenly their keen ears caught the sound of a motor. Looking up, they plainly made out an airplane in the sky above them.

“That’s Karl!” cried Joe joyously. “I wouldn’t be afraid to bet anything that it is.”

“I sure hope you’re right,” came from Bob. “Gee! Won’t it be swell to see him again?”

“Of course there’s a chance that he won’t see us,” said the other boy. “But I believe he will. He’ll be looking around for us closely. Maybe that’s why he’s here now.”

Bob started, as an ominous thought struck him.

“Do you suppose anything’s happened – to our dads, I mean?” he asked in a tense voice.

Joe’s face darkened.

“I – I hadn’t thought of that,” he replied solemnly.

They watched the airplane closely, expecting at every moment to see it head downward.

Then it came.

“Hurrah!” Bob was overjoyed. “Karl sees us, all right. And it’s Karl, too,” he observed, as the monoplane came closer.

As the machine flew closer it circled around the little group below, rapidly flying lower. When within a hundred feet of them, its cabin window opened, and Karl’s face was thrust out.

“Hello, up there!” shouted Bob, and received an answering greeting. But the noise of the ’plane’s engine made it impossible for the adventurers to understand the aviator’s words.

While the three were still gazing up at the huge monoplane they saw something that caused them to look all the closer. They made out Karl’s arm reaching out of the cockpit. Then they saw something white drop toward the ground.

“It’s a small parachute,” observed Joe, his heart beating rapidly. “Wonder what’s tied to it?”

As there was no wind, the object fell in a straight line, the parachute opened and began to float slowly above the onlookers. Before long it came to the ground within fifteen feet of them. Karl had certainly aimed accurately.

“Hurry!” cried Joe. “Let’s see what it is. Maybe something’s happened to our dads or the others.”

He picked up the parachute, at the end of which was attached a small box. Opening it, the youth found a folded paper.

“Quick!” murmured Bob. “Let’s see what he has to say.”

CHAPTER XXVIII
Almost a Tragedy

RATHER nervously Joe unfolded the paper, hastily read it, and then gave a sigh of relief.

“Nothing wrong,” he told his friends. “Take a look.”

“H’m,” observed Bob. “He only says he’s going to land in a level field about a mile from here, and that he’d better take us up with him from there, instead of waiting till we get to Pasaje. No other place near to land on. Closes by saying everything is all right.”

“So he wants us to go up with him now,” mused Joe. “Doesn’t want to wait till we get to Pasaje. I hate to do that. I don’t like to leave Dr. Rander till we get to the town. It doesn’t seem right to come with him all this distance and then go off and leave him here in the mountains.”

“Don’t worry about me,” said the old explorer quickly. “I have been through these mountains alone many times. I can manage the mules all right. And the town can’t be far away.”

“We’d go with you anyway,” Bob told him, “only Karl says there isn’t another landing place near.”

Without loss of time the three continued toward the level spot on which the aviator had landed, at length coming in sight of the monoplane.

Karl rushed out to meet them, his face bright at finding that all were alive and well.

“You old rascal!” cried Joe, shaking the young man’s hand warmly.

“How’d you know we were here?” asked Bob, who was also very glad to see the aviator.

“I saw you,” Karl Sutman explained. “I thought I’d take a short flight over this section to see if I could locate you.”

“You did, all right.” Joe was delighted. “Found us away out here in the wilds.” He hesitated a moment and glanced at Dr. Rander. But the latter had already been introduced to Karl Sutman, and needed no introduction by the youths.

There was one question in the aviator’s mind that he could wait no longer to ask.

“The treasure you were searching for – did you find any?” he inquired. “And the Inca secrets, too. How about them?”

Bob smiled happily.

“We did,” he answered. “Found both the treasure and the secrets.”

When shown the little box of gold trinkets, Karl gasped in astonishment.

“Is that all you found?” he demanded. “I thought there might have been some gold statues, or the like.”

“If there were we couldn’t locate them,” Joe said. “We considered ourselves lucky in finding what we did. They are worth many hundreds of dollars, maybe thousands.”

“Dad and Mr. Lewis and the others – are they all right?” Bob was anxious to learn if any misfortune had befallen his father and friends.

“They’re still hunting for specimens,” returned the aviator. “Mr. Wallace fell down a mountain and hurt himself slightly, but he’s about all right now. And you should see the large collection of birds and animals they have.”

“We have something that may interest them,” declared Joe, and showed Karl the huge condor, at the same time telling about his narrow escape from death.

“Wow!” Karl exclaimed when the youth had finished. “And Bob and Doc Rander came to your rescue, did they? Good for them.”

It was later decided that Bob and Joe accompany Karl at once in the monoplane to the Comberciato River, where the chums’ fathers were collecting specimens. The old man explained that he did not mind going on alone to Pasaje, where he had business.

“But before you leave,” Dr. Rander began, “I want to divide the treasure with you fellows,” addressing Bob and Joe.

“Don’t give us half,” Joe said pleadingly. “After all, it was your efforts that located the secret mountain cavern.”

The old man held up a hand for silence.

“You forget that I owe my life to you,” he reminded them. “If it had not been for your coming to my rescue, I would not be here to enjoy the treasure.”

“But – ” began Joe.

“Say no more,” Dr. Rander silenced him. “Half of the gold is yours.”

He spent the next half-hour in dividing the treasure, giving the boys a good share. They thanked him warmly, then turned to Karl Sutman.

“Can we get started before long?” asked Joe. “I’m anxious to see everybody.”

“Sure.” The aviator was willing. “Let’s get your stuff loaded in the ’plane.”

They worked steadily until noon, at which time everything that belonged to the youths was packed in the supply compartment of the monoplane.

After the meal they bade Dr. Rander an affectionate farewell and stepped into the cabin. Karl started the engine, and then, with a roar and a rush, they started rolling over the field.

The old man waved as they left the ground and headed toward the north. The last the air travelers saw of him he was getting the pack animals ready to finish the journey to Pasaje.

“I suppose we’ve seen the last of him,” remarked Bob, as they left the ground. “We may hear from him later, though. He has our addresses.”

“Rather an odd character, isn’t he?” said Joe. “Seems strange that he’d want to remain in these mountains all his life.”

During the next few hours Karl sent the airplane ahead over mountains that were more rugged than any the youths had ever seen before. He was steering the machine near Mount Panta and the locality in which were Dr. Rust and the other archæologists when suddenly he found himself almost unconsciously entering a heavy cloud.

A second later, when he realized what he had done, the aviator saw that it was too late. Already the ’plane was in the midst of a heavy opaque atmosphere of white.

“I was a nut for getting in a place like this,” Karl said through the telephone. “And there’s no way of getting out now only to go on through it.”

Karl well knew that they were in grave danger of crashing into the side of some lofty peak. They were in a region of tall mountains, and some high summit might easily loom up before them.

For the next few minutes the youths’ hearts were in their mouths. They knew that Karl was an excellent pilot, but they also knew that he could do nothing if sudden tragedy might come upon them.

“What’s that?” cried Bob quickly. He had seen something that looked like a huge black mass directly before them.

Joe sat on the edge of his seat, expecting every moment to feel a terrible crash and then… For the first time he wondered what death was like.

Cries of relief came from the youths as they saw that instead of crashing into the black mass, they were passing through it.

“As if a million pounds were lifted off my back,” gasped Joe. “I thought we were goners sure.”

“Would be if that were a mountain,” Bob said. “As it is, we’re no worse off than before. It’s a lot darker, though.”

Karl sought to pass out of the cloud by gaining altitude, but he soon saw that this was useless. Still, he thought it best to fly higher. There was a limit to the height he could safely reach, however, for neither himself nor the youths were using oxygen, and the high rare air was not sufficient to supply enough necessary to the human body.

“I’ll have to trust to luck, I guess,” he said through the telephone. “We may make it all right.”

“Karl didn’t say that any too hopefully,” remarked Joe. “Do you suppose he really fears disaster?”

“It seems like it.” Bob was terribly worried. He did not have much hope of getting out unharmed.

Then suddenly the air travelers received a surprise. The cloud that had a few seconds before been so heavy and dense quickly thinned out until it passed from view. Once more the blue sky was visible.

The explorers could hardly believe their eyes. Had they actually emerged from what seemed like certain disaster? It was some time before anyone spoke.

“What do you think of that one?” Karl Sutman’s voice was the first to break the silence. “Couldn’t have been much worse suspense, could there?”

“We didn’t see that we had much chance,” said Joe gravely. “And when we saw that black mass – ”

“We’re out of it now, though,” the aviator said. “So why not dismiss it from your mind?”

He was put out to think that the monoplane was several miles off its course, but he refused to let that worry him, since they had had such a miraculous escape.

It did not take long, however, to make up for the lost time, for the young pilot well exceeded the hundred-and-fifty-mile-an-hour cruising speed of the monoplane.

As best he could he kept the machine as near the mountain tops as was safe, so as to make it unnecessary to use oxygen. Getting out the masks and tanks would require much time, and that was what they did not want to spare.

“There’s Mount Panta,” observed Joe, his eyes on a massive peak. “Why can’t we stop and see the archæologists – for only a few minutes, I mean? I suppose they’re still looking for Inca ruins in this region, aren’t they?”

“Yes and no,” laughed Karl. “I mean this: they’re still searching for ruins, all right, but not in this part of the Andes. I stopped to see them just before I flew after you fellows, and they told me they were going to leave for another section over to the east.”

“Wish we could have got in touch with them,” said Bob. “We have information about Inca secrets that would make them jump up and down with joy. Maybe we can tell them later, though.”

A half-hour of flying from Mount Panta brought them within sight of the Comberciato River, along whose banks somewhere the youths’ fathers and Mr. Wallace were staying.

Suddenly Bob and Joe cried out in delight.

“Dad! Mr. Lewis! Mr. Wallace!” said Bob happily.

CHAPTER XXIX
The Horrible Beast

THE joy of Bob and Joe at seeing the naturalists was certainly great. After those strenuous weeks in the mountains, the youths had been growing anxious to be with their fathers and Mr. Wallace again. Now, as they viewed the men waving at them from below they were overly anxious to land.

There was a wide open place directly under them, and to this Karl sent the monoplane. When finally it came to a stop, Bob and Joe dashed out and ran to meet their fathers and the scientist from Chicago.

“Boys!” cried Mr. Holton, too joyful for words.

He and Joe’s father and Mr. Wallace fairly ate the youths up in their happiness at seeing them alive and well.

“You came through all right, I see,” laughed Mr. Lewis, after the first few remarks were over. “What kind of a time did you have? And the treasure – did you find any?”

“Look,” returned Joe and showed them the box of gold beads.

The men cried out in astonishment. Unlike Karl Sutman, they had expected the youths to return without having found anything of value.

“You were successful, all right,” observed Mr. Holton. “Tell us about your adventures.”

While the men listened intently, the boys related their experiences from the time they had left Cuzco with Dr. Rander.

When at last they were finished, the naturalists shook their heads gravely.

“It was all very interesting, but at the same time it was dangerous,” said Bob’s father solemnly. “Afterward we wished you fellows hadn’t gone.”

“But they came through all right – and brought us a white condor at that,” beamed Mr. Lewis. “No doubt this is the only condor real we’ll see. We did shoot two of the more common kind, though.”

“Did you get many specimens?” inquired Bob.

“Come and see for yourselves,” smiled his father and led the way to the naturalists’ camp.

“Great Scott!” cried Joe, surprised at seeing such a vast number of wild animals and birds. “This region must teem with all sorts of animal life.”

“It does,” returned Mr. Wallace. “And that reminds me. We were going out in search of a black ‘spectacled’ bear this afternoon. We’d like to have you go with us, if you will.”

“Will we?” cried Joe. “Does a cat miaow?”

The naturalists had everything in readiness for the bear hunt. They had but to eat a lunch and then they would be ready to start the hunt.

Mr. Lewis had heard reports from natives that one of the huge animals had been seen in a dense woodland beside the river. To this spot the party went, rifles in readiness.

When they entered the jungle they were met with total surprise. Beside an opening in the hillside was the bear, crouching low for a charge!

There was only a moment to act.

“Shoot!” cried Joe fearfully. His rifle had been dashed from his grasp by a protruding tree bough.

Bob had taken a position a number of yards from the others. He had intended to search another part of the jungle. The youth was holding his gun in readiness now, looking for a chance to take aim.

Then he thought the time had come to fire, and pulled the trigger.

Bang! The rifle spoke, but the bear had suddenly turned, and the bullet missed.

With a snort of rage the huge beast turned on Bob, showing its terrible teeth savagely.

Bob saw the danger and was hurriedly trying to work the bolt on his rifle. But unfortunately the mechanism had jammed.

Helpless, the youth would be at the mercy of those terrible teeth and claws! Already he could imagine the horror of what would follow.

Bang! Bang! Two rifles barked, and each bullet found its mark. Another shot and the huge bear fell dead, almost at Bob’s feet.

“Whew!” gasped Karl Sutman, holding his smoking rifle. “Another narrow escape to add to you fellows’ already long list.”

“We’re piling ’em up thick and fast,” said Bob. He could laugh, now that the danger was over.

They made their way back to camp, after having cut off the great skin. It was at once placed in preservative.

“One more prize specimen to add to our collection,” said Mr. Wallace. “I’m betting that Bob and Joe will prove a valuable asset to the expedition during the next few weeks. They’re both good shots, and they have plenty of courage.”

Indeed the youths tried to justify themselves of this tribute, and were successful in doing so. During the eventful days that followed they collected many specimens for the scientists, including about every form of life they could see in this wild region. Often they made long excursions into the adjoining mountains in search of new wild creatures, and usually found them. Taking moving pictures also occupied their time.

But although the naturalist party was meeting with success in its search for fauna, the men did not wish to remain here too long, for other duties at home prevented it. Especially was Mr. Wallace anxious to get back to Chicago.

It was arranged one day that he and Bob and Joe go with Karl Sutman in the monoplane back to the United States, preceding Mr. Holton and Mr. Lewis, who would arrive later by steamship. The youths’ fathers took it on themselves to attend to getting the specimens on muleback to the coast, where they would be loaded on the vessel.

The four leavetakers were given an affectionate farewell by Mr. Holton and Mr. Lewis, who expressed hope that their sons and friends would arrive in the United States without mishap.

On the way to the coast the air travelers stopped to see Dr. Rust and others of the archæologist party. Bob informed them of the Inca secrets he and his friend had found, and gave them the map he had made of the region. The scientists’ delight far exceeded the boys’ expectations. They literally mauled the youths in their intense enthusiasm.

When the chums, Mr. Wallace, and Karl climbed into the cabin, the scientists gave them a royal send-off, wishing them a safe journey.

And safe it proved to be. Karl’s ability as a pilot was greatly appreciated as they flew toward the United States, which they reached without incident.

“Now to get home,” said Bob, as he and Joe and Mr. Wallace hailed a taxi. The naturalist intended to spend another day or so with the boys before boarding a train to Chicago. Karl Sutman left them at the airport, promising to get in touch with them within the next few days.

At their homes Bob and Joe and their friend were given a profound welcome by Mrs. Holton and Mrs. Lewis, who were desirous of knowing about their experience.

“We had a wonderful time,” said Joe, as they all sat in the Lewis living room. “And we met with adventures aplenty. There’s nothing quite like exploration, especially when you’re looking for ancient secrets.”