“LET go!” cried Bob, in his excitement forgetting that the Indians could not understand English.

The group had completely surrounded the youths, and one man was holding tightly to Bob’s camera.

The two chums knew that they had little chance against so many. But they fought doggedly to save the moving-picture machines, which were the only two they had.

With one supreme effort, Bob pushed the Indian nearest him to the ground and turned to find an opening in the crowd of natives.

But they were all about him, pushing and grabbing and striking to the best of their ability. It was plain that they were determined to take possession of the small boxes that the whites carried.

If it had not been for the necessity of holding onto the cameras, Bob and Joe could have put up a good fight, and perhaps driven the Indians away. But as it was they found themselves at a sore disadvantage.

“Help!” cried Joe, raising his voice to a shout. “Help! Help!”

Several seconds later a figure showed itself at the brink of the hill and came toward the fighting group.

“It’s Dad!” Joe cried happily. “Now there’ll be a fight!”

Mr. Lewis was soon joined by Mr. Holton and Karl Sutman. Like a flash the three grasped the meaning of the scuffle and rushed to the aid of the chums.

They dived headlong into the furious mob, using their fists to great advantage. One big fellow Mr. Lewis knocked flat on his back in a daze.

“Here, take my camera,” directed Bob, speaking to Karl. “Run as fast as you can back to camp. I want to take a lick at some of these beggars.”

Karl did as asked and dashed out of the mob for the tents. The last Bob saw of him he was rounding a bend and heading toward the monoplane.

Then Bob faced the man who had grabbed his camera.

“Take that!” the youth snarled, sending the Indian crashing to the ground.

The other natives, seeing that they were unable to hold their own against these whites, took to their heels and disappeared in the distance, kicking up a cloud of dust behind them.

“Well, we licked them.” Mr. Lewis was panting for breath. His face was red from fatigue, his clothes torn and wrinkled.

And the others were no better off. They had put up a game fight, determined to drive away their enemies.

“What was their motive for attacking you?” inquired Mr. Holton, wiping his face with his handkerchief.

“Beyond us,” Joe answered him. “We just looked at them and pointed our cameras at them——”

“Oh.” Mr. Holton seemed to understand everything. “That’s all you did, huh? Well, you did enough to excite their anger. Those natives are decidedly against having their pictures taken. They believe that any evil which might befall their pictures will come upon them later.”

“So that was it?” Bob laughed. “Well, we’ll know enough not to try the same thing again. Anyway, we got several feet of film exposed, and that’s better than nothing.”

The adventurers made their way down the hill, to be met by Karl and the others of the expedition, who had come to learn of their friends’ misfortune.

“Quite an encounter,” commented Mr. Dunn, when he was told the details. “These Indians are bad characters when their anger is aroused.”

Back at the camp, the explorers got everything in readiness for the expedition to depart as soon as Mr. Wallace, Dr. Rust, and Professor Kelley returned with the mules and guides.

It was nearly noon when Bob caught sight of a long line of mules heading toward the camp. They were coming slowly and leisurely, but always closer. Near the rear were the three explorers and two natives, who had been driving the animals.

“I see you met with success,” said Mr. Buenagel, addressing Mr. Wallace.

“Success is right!” the naturalist was beaming all over. “Don Chusmena here”—indicating a small Peruvian who had been conversing with several natives—“has generously offered to let us use twenty of his mules. They are all fine specimens, worthy of making the mountain trip. And the price is right.”

The mules were driven up to the camp and herded together in a group.

Mr. Wallace introduced Don Chusmena to the others. The Peruvian in turn acquainted the Americans with the Indians who were to act as guides for the expedition. He assured them that the natives knew every foot of ground in the Andes country. One Indian was to lead Dr. Rust and the other scientists who were to search for Inca ruins. The other native would guide Mr. Lewis and any others that might be in the party of naturalists.

Both Bob and Joe had decided to stay with the expedition and not fly in the monoplane with Karl Sutman. Mr. Holton, however, intended to accompany the aviator and Dr. Brown, the expedition’s physician. Karl and the two men were to fly on ahead and look for Inca ruins from the air, keeping in touch with the others. It was intended that Karl head for the valley of the Comberciato, where he and Mr. Holton and the physician would await the others of the naturalist party.

“That leaves you and Mr. Wallace and Dad and I together,” remarked Joe. “I’m sorry your father isn’t going with us.”

Bob nodded.

“He’ll meet us at the Comberciato River, though,” the youth said.

“But that won’t be until two weeks from now, at least.” Joe would have been better satisfied if Mr. Holton had intended to go on foot instead of in the airplane.

Mr. Lewis and Mr. Wallace desired to get their division of the expedition started as soon as possible. But since it was so late they thought it best to wait until the next morning.

“That’ll give us time to look around some more,” said Joe, picking up a motion-picture camera. “Come on, Bob. There’s a lot to be seen around Cuzco.”

“Be careful boys,” warned Mr. Holton. “Don’t try to photograph any more Indians, or you may get into a bigger scrape than the one this morning.”

“Leave it to us,” laughed Joe. “We’ll be all right.”

The youths headed west toward the river Almodena. They resolved to cross it and proceed northward to the Fortress of Sacsahuaman and other Inca ruins.

From the river there was a narrow road that led up the plateau to the high hill that overlooked the city. As this hill stood between the boys and the ruins of the fort, which were located high upon another cliff, they found it almost necessary to climb to the top and then down the other side.

“Now for the ruins,” said Bob eagerly, pointing to the top of the low mountain that was before them.

The youths had begun the difficult climb to the summit and had rounded a turn in the rocks when they caught sight of an old man climbing slowly up the dangerous ridge.

“Look!” cried Joe in terror. “He’s falling!”

The old man’s foot had slipped, and he was trying as best he could to balance himself on a narrow ledge.

His efforts were in vain. The next moment he began to plunge helplessly downward.

With the quickness of a cat, Bob stepped forward and, bracing himself as best he could, he threw himself against the man. The impact of Bob’s heavy body stopped the man’s fall and sent him against the side of the cliff. It bruised his face and shoulders, but he was safe.

After a few moments of resting, the old man looked up, wild-eyed and white with fear. There was an expression of intense gratitude on his wrinkled face as it was turned toward Bob.

“You saved my life!” he cried in excellent English, gazing fearfully below. “And I want to reward you. I want to tell you of some Inca secrets—secrets of the Andes!”