"But the fleet--it's approaching Abaco," d.i.c.k cried. "I've got to warn them."

Fredegonde seized him by the arm.

"Come with me," she cried. "If they find you here, they'll kill you."

d.i.c.k hesitated only a moment, then followed the girl as she dashed for another door on the same side of the laboratory as that by which Von Kettler and his men had fled. They dashed down the staircase, and a corridor disclosed itself at the bottom. The girl stopped.

"There is a private way--the Emperor's," she panted. "He had it constructed--in case of necessity. I got the keys. I was planning--something desperate--to stop these murders; I didn't know what."

d.i.c.k seized her by the arm. "What keys?" he demanded. "The key to the place where President Hargreaves is?"

"Yes, but--"

"We must get him. Where is he?"

"In a cell beneath the throne room. That's overhead. But they'll catch us--"

"Which is the key?" asked d.i.c.k.

The girl produced three or four keys, fumbled with them, handed one to d.i.c.k. "This way!" she cried.

They ran along the corridor. Two guards appeared, moving toward them under the electric lights. At the sight of the girl running, and Luke Evans, they stopped in surprise.

d.i.c.k had pulled the hood back over his head. He ran toward them, wielding the iron bar. A mighty swing sent the two toppling over, one unconscious, the other bruised and yelling loudly.

"Here! Here!" gasped Fredegonde, stopping before a door.

d.i.c.k fitted the key to the lock and turned it. Inside, upon a quite visible bed, sat President Hargreaves, unchained. He looked up inquiringly as the three entered.

"Mr. President," said d.i.c.k, throwing back his hood, "I'm an American officer, and I want to save you. There's not much chance, but, if you'll come with me--"

Hargreaves got up and smiled. "I'm not a military man, sir," he answered, "but I'm ready to take that chance rather than--"

He did not complete the sentence. Shouts echoed along the corridor behind them. d.i.c.k replaced his hood, handed the keys back to the girl.

"Take Mr. Hargreaves to any place of temporary safety you can," he said. "And Mr. Evans. I'll hold them!"

"It's right here. This door!" panted the girl, indicating a door at the end of the pa.s.sage.

The three ran toward it. d.i.c.k turned. Five or six guards with Von Kettler at their head, were running toward him. They saw the three fugitives and set up a shout.

d.i.c.k had a quick inspiration. He dashed back into the cell, seized the light bed, and dragged it through the doorway into the pa.s.sage, just in time to send Von Kettler and two others sprawling. He brought down the bar upon the head of one of them, shouting as he did so.

Then he became aware that the pa.s.sage was flooded with sunshine.

Fredegonde had got the door open.

He darted back, pa.s.sed through in the wake of the three, and slammed it shut. Fredegonde turned the key. Instantly d.i.c.k found himself with his three companions upon the prairie. Not a vestige of the buildings was apparent anywhere, except for the patches of brown earth.

CHAPTER XII

_Von Kettler's End_

Fredegonde took command, repressing her agitation with a visible effort. "They cannot break down that door," she said, "and they dare not ask for another key. It will take them a minute or two to go back and reach us around the building. But there may be a score of people watching us. Let us walk quietly toward the thickets. If I am present, they will not suspect anything is wrong."

But d.i.c.k stood still, driven into absolute immobility by the conflicting claims of duty. For overhead, high in the blue, was an American dirigible.

And at his side was the President of the United States. One or other of them he must sacrifice.

He chose. He ran forward without answering. Those squares of brown earth, set side by side, were the airplane hangars, and he meant to seize an airplane, if he could find one beneath its coat of invisibility, and fly to warn the dirigible and the fleet.

A curious wind was blowing. It seemed to come swirling downward, as no wind that d.i.c.k had ever known. It was growing in violence each moment, beating upon his face.

As he ran, he was aware of Luke beside him. He heard shouting all about them. Luke had been seen. Not only Luke, but Hargreaves, who was running after Luke, with Fredegonde trying in vain to change his intentions. At the edge of the first brown patch d.i.c.k collided violently with the wall of the invisible hangar, and went reeling back. The shouts were growing louder.

"Wait!" gasped Luke Evans. He had something like a large watch in his hand. He held it out like a pistol, and from it projected a beam of the black gas.

Then d.i.c.k remembered Colonel Stopford's words: "He showed me a watch and said the salvation of the world was inside the case. I thought him insane."

Insane or not, old Luke Evans had concealed the tiny model of the camera-box to good purpose. As he swept the black beam around him, the whole ma.s.s of buildings sprang into luminosity, the figures of a score of men, grouped together, and advancing in a threatening ma.s.s, some distance away--and more.

Two airplanes, standing side by side upon the tarmac, just in front of the hangar--not mere pursuit planes, but six-seaters, formidably armed, with central turrets and bow and rear guns, and propellers revolving.

Two mechanics stood staring in the direction of the little group.

"I'm with you," gasped Hargreaves. "I'm not a military man, but I've got fighting blood, and I come of a fighting race."

d.i.c.k leaped and once more swung the iron bar. The nearer of the two mechanics went down like lead, the second, seeing his companion bludgeoned out of the air, turned and ran.

d.i.c.k shouted, pointing. Fredegonde jumped into the plane, and the President scrambled in behind her. The group, dismayed by the black beam, which Luke Evans was now turning steadily upon them, had halted irresolutely. But suddenly a head appeared, moving swiftly through the air toward the plane. It was Von Kettler, with hood flung back, the face distorted with rage and fury.

At his yells, the whole crowd started forward. d.i.c.k leaped into the central c.o.c.kpit, swung the helicopter lever. Something spitted past his face, and a long streak appeared on the turret, where the gas-paint had been scored. But he was rising, rising into that increasing wind....

He heard a yell of triumph behind him. And that yell of Von Kettler's was his undoing. There is the telepathy between close friends, but there is also telepathic sympathy between enemies, and in an instant d.i.c.k understood what that shout of triumph portended.

He was rising into the line of magnetic force that would anchor his airplane helplessly, and leave it to be jerked down and held at Von Kettler's mercy.

He released the helicopter lever and opened throttle wide. For an instant the heavy plane hung dangerously at its low elevation, threatening to nose over. Then d.i.c.k regained control, and was winging away toward the sea, while yells of baffled fury from behind indicated the chagrin of his enemies.

He glanced up. Thank heaven the dirigible had not approached the trap.

It was apparently circling overhead. Of course the observers had seen nothing, had no conception that the headquarters of the Invisible Empire lay below.

And yet it seemed to be drifting aimlessly back toward the fleet--erratically, as if not under complete control. And d.i.c.k could see the ships about a mile offsh.o.r.e, apparently drifting too. They were moving as no American squadron ever moved since the day the first hull was launched, for some of them, turned bow inward toward others, seemed upon the point of collision, while others were lagging on the edge of the formation, as if pointing for home.