Joan shook her glossy hair as Epworth sat up and looked around, and twisted her eyebrows in a puzzled way.

“It came out of that round black tube buried in earth at the far side of the valley; or, perhaps, it was one of the mysterious flying machines that the newspapers talked about—like the one that captured the Greyhound. You can readily see that this is the lair of the sky bandits. There is the Greyhound.”

Epworth drew out his powerful field glasses. He never failed to carry them with him. In fact, he had become so accustomed to searching the earth for miles around as he flew over it that it had become as much of a habit to carry binoculars as it was to wear his nose. His observations corroborated Joan’s statement concerning the Greyhound. In addition to that plane he saw a number of other machines that belonged to the Atlantic-Pacific Airlines, Inc., and bags of saltpeter piled indiscriminately around a large warehouse made of corrugated iron.

But there were no indications of idleness in the camp. Even the women and children were doing some kind of work, and the men—more than a thousand of them—were rushing pell mell hither and yon, gathering up large quantities of stuff, pushing it into containers, and piling the containers systematically into cylinders at least two thousand feet long.

“No, it was not an airship. It was one of those long aluminum cylinders that are being loaded by the men at work. It was shot up into the air by some kind of machinery. But why do they do it, and where is the machinery?”

“In that hole in the ground,” Joan explained, as she glanced through the binoculars. “There seems to be a round pit over there.”

“Well, we are going down there and find out what it all means. Very likely the crews of all the airships stolen are down there. I am quite sure that Billy Sand is there.”

“Going to walk right in, turn right around, and walk right out with all the airships and the rescued crews?”

Her tone was quite sarcastic.

“I hardly think that we will work that fast but if we are not able to sneak into that place and get the Greyhound there is very little hope of ever returning to dear old Uncle Sam.”

“There are forty of the new-style airships,” she pointed out, “and it would be easy for them to overtake the Greyhound.”

“We will have to risk something. We will never——”

He was stopped by a giant cylinder being catapulted out of one of the dark tubes, and flashing away into space. They stood staring for fifteen minutes, and another cylinder followed. Then the hum of the machinery quieted down. Epworth drew out his watch. “It has been just ninety minutes since the first cylinder was fired,” he asserted. “The second the cylinder goes into space the men below get awful busy loading another. They are—yes, I really believe that they are systematically shooting something into space.”

“Are they crazy?” Joan looked around apprehensively. “I would rather run into a nest of robbers than a camp of crazy people.”

“We will try to get down there, and get away without being seen. Around the side of the cliff I see a place where it will be possible to slip down without hurting ourselves, although it is steep.”

“I don’t like the looks of things down there,” his sister objected. “Look at that ugly giant!”

She gave Epworth the field glasses, and pointed to a certain man. He was a great giant, long-bearded, hairy, and powerful. He was viciously whipping a smaller man while four men held the small man a prisoner with his face to the wall of a big corrugated iron building.

“Slave drivers,” Epworth observed sharply, his mouth twitching angrily. “I wonder if the little fellow can be Billy?”

Joan shuddered. She was thinking of the gallant young aviator flying away into the night to give himself voluntarily into captivity for the sake of the men who employed him—a captivity that at present looked as if it was the most vicious of all tyranny.

“We’ve got to get away, and send help,” she whispered fiercely. “This racket must be cleaned out if it takes the entire United States army.”

“The United States army cannot come into this country. It is foreign soil. The easiest thing to do is to steal the plane.”

“I’ll venture there are a thousand eyes watching it.”

“You’d throw cold water on a fish,” Epworth grumbled. “But just the same we shall make the attempt.”

At this moment a door in one of the large corrugated iron buildings opened, an enormous cylinder was rolled out, twenty men got aboard, and it shot up into the air with incredible rapidity.

“How would the Greyhound get away from an airship like that?”

Joan’s eyes fastened on the disappearing ship with intense fascination.

“I do not see any propellers,” she added thoughtfully.

“It is a rocket plane, I previously described, the latest improvement on the German idea of shooting an airship forward with liquid rockets. However, let’s be moving.”

They ate from the lunch boxes that Epworth had hastily snatched up when they jumped into the air, and with stealthy steps descended the steep incline, hiding frequently behind the large boulders on the hillside. Fortunately the men in the valley, or rather huge crater—for it was patent that it had one time been a volcano and the fires were only now simmering in spots—were busy and did not see them, and they finally got safely behind the large hangar that protected twenty or more of the big airships. Inside of the building the men at work were talking in a strange language but when Epworth peeped around the corner he discovered the coast to the Greyhound seemed clear.

Slipping from behind the hangar they darted across the open space, and gained the protection of another building without being seen. Repeating this maneuver several times they finally came up to several of the American planes. But they had been purposely battered. A wing had been destroyed, an engine had been put out of running, the propeller had been broken, or the fuselage and rudders shot to pieces. The Greyhound had not been in camp long, and seemed to be in working condition. They centered their attention on it.

First Epworth surveyed the field. The crater pit was swarming with men, and weaving in between them were hundreds of women and children. Obviously it was some kind of a colony, and Epworth caught himself wondering what all these people meant by coming this far from civilization to live.

Some distance away the young man saw a body of American aviators. They were shoveling saltpeter into an enormous vat, and were being herded around by heavily armed guards. Frequently a heavy whip was used on the back of a prisoner to expedite his movements.

When Epworth saw this he realized that it would not be long before the Greyhound would be dismantled. The pirates did not intend to give the prisoners a chance to escape.

Again he gave the Greyhound a careful study. It was guarded by four men who were seated on a boulder on the side of the mountain opposite from his possible approach. He and Joan would have to get to the Greyhound, get in it, rev up, and get away with a swiftness that was almost an impossibility.

Still it was their only chance. He would make a stagger at gaining his liberty. If they remained in this crater it would be only a matter of a short time before they would be discovered.

To make the break Joan must go also, and it would be hard to slip into the plane without one of them being seen.

“Concealment is useless,” he asserted. “We must run for it. When you get there jump in, and if we are attacked I will try to hold them off while you start the engine.”

Fleet as swallows the two darted forward. Epworth, an all-round athlete, timed his speed to keep even with the girl. They got to the door, Joan’s hand was on it, when the four guards ran around the plane, gave a shout and closed in on them.

“Jump in!” Epworth urged. “Snap at it. I will hold them.”

He whirled like a lion, dodged, and caught the leading guard a heavy blow in the stomach. The man doubled up with a grunt, and Epworth, foot-working swiftly and dodging with the expertness of a prize fighter, evaded a rush by two men, and caught the fourth a right hand body blow on the run. His victim toppled over sideways.

Not for a second did he pause. He was fighting for life. These men were unscrupulous robbers. He knew this by the way in which they destroyed airplanes. They would not hesitate to slug him, and make Joan’s future life miserable.

Wheeling fiercely he flung himself on the other two men. This time he made a football rush, jerked a man’s legs from under him, and crashed his head against the ground. Before the other man could catch him he bounded to his feet, and struck him a vicious blow under the chin. The man toppled like a tenpin.

All this time the man he had punched in the stomach was doubled up groaning. Now he lifted his head, and straightened up. But before he could advance Epworth bounced forward, leaped into the open door of the Greyhound, and dropped into the aviator’s seat, panting from his violent exertion.

The next second the Greyhound was spluttering loudly and taxying across the rocky ground. If the engine would pick up a little safety was in sight.

It did. After popping loudly for several seconds it purred down and the Greyhound lifted its wheels from the ground.

At this moment a huge giant stepped out of the most pretentious house in the place. In his hand he held a light machine gun. Leveling it at the Greyhound he began to shoot. There were three propellers, and one by one, with uncanny aim, the giant disabled the blades and just as escape seemed at hand the airship staggered, slumped like a wounded bird, and struck the ground with powerful impact.

Joan, seeing inevitable fall, braced herself with her feet, and escaped with a slight jar.

Epworth, in a vain attempt to lift the nose of the ship upward, was hurled against the cowling with a force that knocked him unconscious.