He stood there, his face muscles working as he shouted for his companion, but no sound came from his lips. He looked about him, and saw the unconscious man beside the window. He started in his direction.

With a shout, d.i.c.k hurled himself toward him. And he checked himself even as he was about to leap. For he realized that the second workman neither saw nor heard him.

Yet some subconscious impression of danger must have reached his mind, for the workman stopped too, instinctively a.s.suming an att.i.tude of defense. d.i.c.k gathered a dozen links of his wrist-chain in his right hand, leaped and struck.

The workman crumpled to the floor, a little thread of blood creeping from his right temple.

It was the thing upon which d.i.c.k looked back afterward with less satisfaction than any other, leaving the two unconscious men in that room of death. Yet there was nothing else he could have done. He ran to the trap, and saw a ladder leading down. In a moment he had swung himself through and closed the trap behind him.

The material that lined the walls below must have had almost perfect insulating qualities, for the temperature here was no hotter than in the Bahamas on a hot summer day. d.i.c.k scrambled down the ladder and found himself in a machine-shop. n.o.body was there, and tools of all sorts were lying about, as well as machinery whose purpose he did not understand. A pair of heavy pliers and a vise were sufficient to rid d.i.c.k of his wrist and ankle chains in a minute or two. With a knife he slashed the cords of invisible stuff that bound him. He stood up, cramped, but free.

He picked up an iron bar that was lying loose on a table beside a machine, and advanced to the staircase in one corner of the shop. As he approached it, another workman came running up.

d.i.c.k stood aside in an embrasure in the wall partly occupied by a machine. The man pa.s.sed within two feet of him and never saw him. Only then did d.i.c.k quite realize that he was actually invisible.

The moment the man had pa.s.sed him, d.i.c.k ran to the staircase. He descended one flight; he was half way down another when a yell of pain and imprecation came to his ears. He knew that voice: it was Luke Evans's!

With three bounds d.i.c.k reached the bottom of the stairs. He saw a large room in front of him. No mistaking the nature of this room; it was an ordinary laboratory, fitted out with the greatest elaboration, and divided into two parts by paneling. And sight and sound were on.

In the part nearer d.i.c.k three men were grouped about a large dynamo, which was sending out a high, musical note as it spun. Levers and dials were all about it, and above it was the base of the gla.s.s tube that d.i.c.k had seen above. In the other part were five or six men.

Three of them were testing some substance at a table; three more were gathered about old Luke Evans, whose silver chains had been removed and replaced by ropes, which bound his limbs, and also bound him to a heavy chair, which seemed to be affixed to the ground. One of the three had a piece of metal in a pair of long-handled pliers. It was white hot, and a white electric spark that shot to and fro between two terminals close by, showed where it had been heated.

d.i.c.k started; he recognized one of the three men as Von Kettler. He moved slowly forward, very softly, his feet making no sound on the fiber matting that covered the floor.

"Did that feel good, American swine?" asked Von Kettler softly, and d.i.c.k saw, with horror, a red weal on the old man's forehead. "Now you are perhaps in a more gracious mood, Professor? The unknown isotope in that black gas of yours--you are disposed to give us the chemical formula?"

"I'll see you in h.e.l.l first," raved old Luke Evans, writhing in his chair.

Von Kettler turned to the man holding the white-hot metal, and nodded.

But at that moment a door behind Evans's chair opened, and Fredegonde Valmy appeared in the entrance. Von Kettler turned hastily, s.n.a.t.c.hed the pliers from the man's hand, and laid the metal in a receptacle.

But the girl had seen the action. She looked at the weal on Luke's forehead, and clenched her hands; her eyes dilated with horror.

"You have been torturing him, Hugo!" she cried.

"Freda, what are you doing in here? Oblige me by withdrawing immediately!" cried Von Kettler.

"Where is Captain Rennell?" the girl retorted. "I will know!"

"He is upstairs, watching the approaching Yankee fleet, and waiting to see its destruction," returned the other.

"You are lying to me! He has been killed, and this old man has been tortured!" cried Fredegonde. "I tell you, Hugo Von Kettler, you are no longer a half-brother of mine! I am through with you!"

"Unfortunately," sneered Von Kettler, "it is not possible to dispose of a family relationship so easily."

"It is cheap to sneer," the girl retorted. "But you sang a very different song when you were in the penitentiary, in terror of death, and you begged me to come and throw you the invisible robe through the bars. You promised me then that you would abandon this mad enterprise and come away with me. You swore it!"

"I have sworn allegiance to my Emperor, and that comes first,"

retorted Von Kettler. "Oblige me by retiring."

"I shall do nothing of the sort," cried the girl hysterically. "When you used me as a tool in your enterprises in Washington, you played upon my patriotism for my conquered country. I thought I was undertaking a heroic act. I didn't dream of the villainy, the cold-blooded murder that was to be wrought.

"You've kept me here virtually a prisoner," she went on, with rising violence, "an attendant upon that old madman, your Emperor, and his sham court, while more murder is being planned. Where is Captain Rennell, I say?" She stamped her foot. "I demand that he and this old man be set at liberty at once. Hugo," she pleaded, "come away with me.

Don't you see what the end must be? This is no heroic enterprise, it is wholesale murder that will arouse the conscience of civilized mankind against you! Order that the vortex-ray be turned off," she went on, looking through the opening in the part.i.tion toward the dynamo. "That gas--you cannot be so vile as to send it forth again, to destroy the American ships?"

"My dear Freda," retorted the young man coolly, "the vortex-ray is already charged with the gas, and at a height of twenty thousand feet it is now creating a vacuum that will send the gas upon the wings of a hurricane straight up the Atlantic seaboard. It will obliterate every living thing on board the battleships, from men to rats, and this time we mean to reach New York.

"As for that swine Rennell," he went on, "you heard His Majesty announce his intention of sending him back to Washington with the information of our irresistible power. Of course I know you are in love with him, and that these qualms of conscience are due to that circ.u.mstance."

But d.i.c.k hardly heard the latter part of Von Kettler's remarks.

Suddenly the significance of the dynamo and the superheated room above had come home to him. He had read of such a project years before, in some newspaper, and had forgotten about it until that moment.

By sending a high-tension current almost to the limits of the earth's atmosphere, the article had said, a vortex or vacuum could be set up which would create a hurricane.

The tremendous pressure of the in-rushing air would make a veritable cyclone, which, taking the course of the prevailing winds, would rush forth on a mission of widespread disaster.

And on this hurricane would go the deadly gas, infinitely diluted, and yet deadly to all life in its infinitesimal proportion to the atmosphere.

And the American fleet was now approaching the Bahama sh.o.r.es.

d.i.c.k forgot Luke Evans, everything else, as the significance of that mechanism in the next room came home to him. He ran like a madman through the s.p.a.ce in the part.i.tion, and, raising the bar aloft, brought it thudding down upon the dials, twisting and warping them.

He struck at the hollow pole, but, gla.s.s or not, it defied all his efforts. He seized a heavy lever and flung it into reverse--and two others.

Yelling, the three attendants broke and ran. Out of the laboratory the six came running, collided with the three. Behind them d.i.c.k could see Fredegonde Valmy, a knife in her hand, slashing at Luke Evans's bonds.

d.i.c.k swung his bar and brought it crashing down on a head, felling the man like a log. He saw Von Kettler pull one of the gla.s.s rods from his pocket and fire blindly. The discharge struck a second attendant, and the man dropped screeching, his clothes ablaze.

Somebody yelled, "He's there! Look at his eyes!" and pointed at d.i.c.k's face.

d.i.c.k leaped aside and swung the rod again, felling a third man. The others turned and ran. Von Kettler in the van, broke through the door behind Luke Evans's chair, and disappeared.

d.i.c.k ran back to where the old man was standing beside the girl, the discarded ropes at his feet. He flung his hood back. "Luke, don't you know me?" he shouted.

It was creditable to Luke Evans's composure that, though d.i.c.k must have presented the aspect of nothing more than a face floating in the air, he retained his composure.

"Sure I know you, Rennell," replied the old man. "And you and me's going to best them devils yet."