"How did you get back here?" demanded Slavatsky.

"Find out!" snapped Dr. Bird.

The dwarf rose threateningly.

"Speak respectfully to me; I am the Master of the World!" he roared in an angry voice. "Answer my questions when I speak, or means will be found to make you answer. How did you get back here?"

Dr. Bird maintained a stubborn silence, his fierce eyes answering the dwarf's, look for look, and his prominent chin jutting out a little more squarely. Carson suddenly broke the silence.

"That's not the Bird we had here earlier," he cried as he staggered to his feet.

"What do you mean?" demanded Slavatsky whirling on him.

"Look at his hands!" replied Carson pointing.

Slavatsky looked at Dr. Bird's long mobile fingers and an evil leer came over his countenance.

"So, Dr. Bird," he said slowly, "you thought to match wits with Ivan Slavatsky, the greatest mind of all the ages. For a time you fooled me when your double was operated on here, but not for long. I presume you thought that we had no way of detecting the subst.i.tution? You have discovered differently. Where is your friend, Mr. Carnes?"

"Didn't your men leave him in the cabin when you kidnapped me?"

Slavatsky looked at Frink inquiringly.

"He stayed in the cabin if he was in it when we got there," the leader of the kidnapping gang replied. "He got a full shot of lethane and he's due to be asleep yet. I don't know how this man recovered. I left him there myself."

"Fool!" shrieked Slavatsky. "You brought me a double, a dummy whom I wasted my time in operating on. Was the other a dummy, too?"

"I didn't enter the cabin."

Slavatsky shrugged his shoulders.

"If that is all the good the menthium I have injected has done you, I might as well have saved it. It doesn't matter, however: we have the one we wanted. Dr. Bird, it was very thoughtful of you to come here and offer your marvelous brain to strengthen mine. I have no doubt that you will yield even more menthium than Professor Williams did this evening especially as I will extract your entire supply and reduce you to permanent idiocy. I will have no mercy on you as I have on the others I have operated on."

Dr. Bird blanched in spite of himself at the ominous words.

"You have the whip-hand for the moment, Slavatsky, but my time may come--and if it does, I will remember your kindness. I saw your operation on Professor Williams this evening and know your power. I also know that you stole the idea and the method from Sweigert of Vienna. I saw you inject the fluid you drew into Willis' brain. Shall I tell what else I saw?"

It was the dwarf's turn to blanch, but he recovered himself quickly.

"Into the chair with him!" he roared.

Three of the men grasped the doctor and forced him into the chair and Slavatsky started the generator. The violet light bathed Dr. Bird's head and he felt a stiffness and contraction of his neck muscles, and as he tried to shout out his knowledge of Slavatsky's treachery, he found that his vocal chords were paralyzed. Through a gathering haze he could see Carson approaching with an anesthesia cone and the sweet smell of lethane a.s.sailed his nostrils. He fought with all his force, but strong hands held him, and he felt himself slipping--slipping--slipping--and then falling into an immense void. His head slumped forward on his chest and Slavatsky shut off the generator.

"On the table," he said briefly.

Four men picked up the herculean frame of the unconscious doctor and hoisted him up on the table. Carson seized his head and bent it forward and the dwarf took from a case a syringe with a five-inch needle. He touched the point of it to the base of the doctor's brain.

"Slavatsky! Look!" cried Frink.

With an exclamation of impatience the dwarf turned and stared at a disc set on the wall of the cave. It was glowing brightly. With an oath he dropped the syringe and snapped a switch, plunging the cave into darkness. A tiny panel in the door opened to his touch and he stared out into the light.

"Soldiers!" he gasped. "Quick, the back way!"

As he spoke there came a sound as of a heavy body falling at the back of the cave. Slavatsky turned the switch and flooded the cave with light. At the back of the cave stood Operative Carnes, an automatic pistol in his hand.

"Open the main door!" Carnes snapped.

Slavatsky made a move toward the light, and Carnes' gun roared deafeningly in the confined s.p.a.ce. The heavy bullet smashed into the wall an inch from the dwarf's hand and he started back.

"Open the main door!" ordered Carnes again.

The men stared at one another for a moment and the dwarf's eyes fell.

"Open the door, Frink," he said.

Frink moved over to a lever. He glanced at Slavatsky and a momentary gleam of intelligence pa.s.sed between them. Frink raised his hand toward the lever and Carnes gun roared again and Frink's arm fell limp from a smashed shoulder.

"Slavatsky," said Carnes sternly, "come here!"

Slowly the dwarf approached.

"Turn around!" said Carnes.

He turned and felt the cold muzzle of Carnes' gun against the back of his neck.

"Now tell one of your men to open the door," said the detective. "If he promptly obeys your order, you are safe. If he doesn't, you die."

Slavatsky hesitated for a moment, but the cold muzzle of the automatic bored into the back of his neck and when he spoke it was in a quavering whine.

"Open the door, Carson," he whimpered.

There was moment of pause.

"If that door isn't open by the time I count three," said Carnes, "--as far as Slavatsky is concerned, it's just too bad. I'll have four shots left--and I'm a dead shot at this range. One! Two!"

His lips framed the word "three" and his fingers were tightening on the trigger when Carson jumped forward with an oath. He pulled a lever on the wall and the door swung open. Carnes shouted and through the opened door came a half dozen marines followed by an officer.

"Tie these men up!" snapped Carnes.

In a trice the six men were securely bound and Frink's bleeding shoulder was being skilfully treated by two of the marines. Carnes turned his attention to the unconscious doctor.