“KEEP your hands on your guns,” called Dr. Kirshner, as he gazed at the approaching party of Arabs.

There were ten of them, and each armed with a short range rifle, which, although inferior to the guns of the Americans, could do a great deal of damage. In addition to the mounts of the Arabs, there were six or seven pack camels that trailed.

As the caravan came nearer, Tishmak waved and shouted a friendly greeting, but he did not receive the same in return. Evidently the men had no friendly intentions.

Tishmak chattered a moment to Fekmah, who then turned to the Americans.

“They are probably nomad bandits,” Fekmah said excitedly. “Tishmak says we might have fight.”

“A fight!” cried Joe. “Why? Are they going to try to rob us?”

Fekmah nodded.

“Worse, perhaps,” he replied.

“Those fellows would think nothing of killing all of us,” said Mr. Lewis gravely. “So we want to be ready for anything that might happen.”

As the Arabs came nearer, their leader shouted something to Tishmak, whose jaw dropped in surprise and astonishment.

Tishmak turned to Fekmah and conversed rapidly. Then Fekmah translated to the Americans.

“They want two of our camels,” he said nervously.

Dr. Kirshner gasped in amazement.

“Want two of our camels?” he cried, his voice indicating a high state of anger.

“What for?” demanded Bob.

“They say theirs are too much loaded,” Fekmah answered. “Want to spread out packs on more camels.”

“Well, of all the nerve!” exclaimed Mr. Holton. “Tell them to get out of here—and get out quick, or we’ll fill them full of holes!”

Fekmah turned to the Arabs and put Mr. Holton’s command before them. Then an answer came.

“They say they go, but we will be sorry,” interpreted Fekmah, as the men turned their camels in the opposite direction.

A moment later they disappeared behind a low dune, leaving a cloud of dust at their heels.

For a moment there was silence among the explorers. Then Mr. Lewis spoke up.

“I don’t like this,” he said, greatly annoyed. “Those men are likely to slip up on us when we’re not expecting them. And such desperate characters would lose no time in shooting us.”

“But what can we do?” questioned Bob.

“Keep on the lookout is all,” returned Mr. Holton. “But I’d feel much safer if this hadn’t happened.”

The explorers rode on into the oasis and dismounted. It seemed pleasing to see green trees and grass again. They were delighted that good fortune had enabled them to find an oasis at a time when it was wise to stop for a meal and rest.

There was good water not far away, and they drank all they wanted, glad of the chance to quench their rapidly overpowering thirst.

“Now,” began Mr. Holton, “we’re going to have something to eat. But first let’s put up the tents. It isn’t wise to be in such a sun as this.”

The bags of supplies were removed from the camels. Then the tents were taken out and put up by Bob and Joe. Mr. Lewis and Mr. Holton got out the food and soon laid out a delicious meal of canned goods and native products.

“Eat all you want, but don’t gorge yourselves,” cautioned Mr. Holton, as they sat about the tent. “There’s plenty of stuff, but still we must be careful. If we’re to be gone any length of time, we’ll have to use our provisions sparingly.”

They ate quietly, taking it easy in the shade of the tent. The heat of the fierce African sun was somewhat abated by the heavy canvas, which would also serve as a shelter from sand storms, should any come up.

When the meal was over, they sat for a few minutes talking. Then Fekmah got up and went over to the corner of the tent.

“Let us sleep for two or three hours,” he said, curling up on the soft soil. “The sun will soon get so hot that we cannot travel without making sick.”

“Suits me,” agreed Joe. “I feel like I could sleep for two or three days.”

“One of us had better stand guard, though,” said Mr. Lewis. “That bandit caravan might return unexpectedly.”

“I’ll do it,” volunteered Dr. Kirshner. “I’m not sleepy. I’ll just take it easy here and read.”

For the next three hours Bob and Joe slept soundly, forgetting that they were under a scorching desert sun. They were not tired, but were extremely drowsy from the heat.

Then suddenly they were awakened with a start. They looked about wonderingly.

Dr. Kirshner stood over them, holding his rifle in readiness.

“The bandits!” he exclaimed excitedly. “I believe they’re coming!”

Mr. Holton and Mr. Lewis jumped to their feet and grabbed their guns. Cautiously they peered out, holding the flap but a few inches up.

“Where are they?” demanded Bob’s father, while Tishmak and Fekmah ran forward.

“I’m not sure that it’s they,” the archÆologist said. “But I heard camel steps a moment ago, and in this country it is best to investigate before it’s too late.”

A second later Tishmak stopped still and listened. He held up a hand for silence. Fekmah had also caught a sound.

“It’s they,” he whispered. “Camels! They’re coming this way!”

The swishing sound increased, and Dr. Kirshner called his friends together for a plan of defense.

“Chances are those bandits were planning on surprising us while we slept,” he said quietly. “They figured that the time to get the camels they wanted was during our afternoon siesta. But it apparently didn’t occur to them that we would set a guard.

“Now the thing for us to do is get together and give them a real welcome with bullets. They’ll probably come around the back of the oasis, where our dromedaries are grazing. We’ll go around there and hide beside that sand dune. Then when the robbers—and I think that’s who the newcomers are—come, we’ll fire a volley of bullets into the air. If we find we can’t frighten them away, we’ll shoot their camels from under them. Then if that fails, we’ll have to shoot the men.”

The others thought this good advice.

“We must act cautiously, though,” warned Mr. Lewis, as they made their way to the back of the oasis.

When they came to the dune, they crouched down and waited. Tishmak glanced around the corner.

A moment later he drew back, his face scowling. He mumbled quietly to Fekmah.

“They’re coming,” the latter said. “And they are the robbers.”

The swishing of footsteps grew louder, indicating that the Arabs were coming nearer.

“Now!” said Mr. Lewis. “Fire in line, aiming at the sky. Then we’ll see what happens.”

Seven rifles spoke up in rapid succession, a dense cloud of smoke arising.

That the robbers had been totally surprised was certain, for a loud chattering followed. Then the sand was thrown up, and they rode off at lightning speed.

Joe peeped around the corner of the dune.

“They aren’t going far,” he announced, following the Arabs’ movements closely. “They’ve stopped behind that sand hill over there.”

“By George!” exclaimed Mr. Holton. “They’re going to plant a battery, are they? Well, just let them waste their ammunition. We won’t fire until necessary.”

“We may need our bullets to use on those two thieves who stole Fekmah’s map,” said Bob to his chum, smiling.

The explorers waited ten minutes for the robbers to take the aggressive, but they did not.

“Well,” said Dr. Kirshner, turning about, “I’m going over and get our things packed back on the dromedaries. If nothing prevents, we want to get started in a short time now. It is much cooler, and we should cover a good distance by night.”

“We’ll stay here and guard a few minutes longer,” declared Mr. Lewis. “There’s no telling what those fellows may do.”

Suddenly a sound from the opposite direction caused them to turn about. Then their expressions changed.

Not fifty feet down the slope were the robbers, riding at full speed toward the explorers. The Arabs had their rifles in position to fire, which they were undoubtedly intending to do when slightly nearer.

“Quick!” cried Bob, his voice cool but determined. “Fire at them before they get us!”

A moment later he took careful aim and pulled the trigger.

His rifle cracked, and the foremost camel went down, sending its rider sprawling over the ground.

Bang! came the sound of Mr. Lewis’s gun, and another camel fell.

The eight Arabs who were still mounted wheeled about and galloped back hurriedly. As quickly as possible they formed a wide line, one beside the other, until it stretched several rods.

“They’re going to charge!” observed Dr. Kirshner. “Have your rifles in position, and make every shot count.”

When the bandits were confident of their formation, their leader gave the command, and bending low over their camels, they dashed with all speed toward the explorers.

Shots rang out from the Arabs’ pistols, but they were too unsteady to cause any damage.

The explorers’ rifles spoke out, and those of Bob and the naturalists found their marks.

Again the rifles cracked. Three more camels went down simultaneously. Now only two of the animals remained on foot, but they were halted abruptly by their panic-stricken riders.

“Luckily we downed the leader,” remarked Mr. Lewis. “And now,” he added, “suppose we get away from here at once. There will be no danger of those men starving, for this oasis will furnish them with food and drink. They can wait for another caravan to furnish them with more camels.”

Without hesitation the party placed the packs back on the dromedaries and rode off, Tishmak in the van.

A few pistol bullets whizzed past uncomfortably close, but soon they died down as the Arabs saw the futility of their efforts.

“Whew! That was some experience,” remarked Bob, when they were well out of sight of the oasis. “I hope we see no more such fellows.”

“And you’re not the only one,” said Dr. Kirshner, shaking his head. “But the desert swarms with bandits, and it will be strange if we don’t have another such encounter.”

“Maybe we won’t have such good luck the next time,” mused Joe.

“Nonsense!” Bob retorted. “We’ll drive them off the same as we did these men.”

“But you got that wrong,” corrected Mr. Holton, smiling. “They made us get away.”

Bob looked a little sheepish as he saw where he had been caught.

“Well, anyway,” he grinned, “they didn’t get us.”

As they plodded on, the sand became looser than ever before. The dromedaries, however, did not seem to notice the change. They plodded on with the same stiff steps.

After two hours of constant traveling, the adventurers found themselves in a narrow valley between two high sand dunes. The country was gradually losing its level character and was steadily becoming more hilly.

Suddenly Mr. Holton gave a cry of delight and pointed to something not far away.