Even then, they had no easy task. Dr. Bird weighed over two hundred and there was not an ounce of fat or surplus flesh on him. First one, and then the other, of the Russians was thrown off him, but they returned to the attack, unsubdued by the crashing blows which the doctor landed on their faces and heads.

Gradually their ardor began to evaporate. With a sudden effort, Dr.

Bird strove to regain his feet. A crash as of all the thunders of the universe sounded in his ears, and flashes of vivid light played before his eyes. He felt himself falling down ... down....

He recovered consciousness to find his feet shackled and fastened to rings set in the concrete of the cavern wall. His head throbbed horribly. He raised his hands and found a huge b.u.mp on his head, from which thickened blood trickled sluggishly down his cheek. The cavern was flooded with light. On the wall before him, a clock told off the seconds with a metallic tick. He bent down and examined his shackles.

"I'm afraid you can't unfasten them, Doctor," said a sardonic voice.

He looked up to see Saranoff.

"I'm sorry I had to hit you so hard," went on the Russian. "Your half hour of unconsciousness has lessened by that much the time which is yours to indulge in an agony of apprehension. Look."

Dr. Bird's gaze followed the Russian's finger. On the floor, twenty feet from where he was shackled, stood a yellow can with the mark of the Bureau of Standards on its side. He recognized it at once as a radite container, a can of the terrible ultra-explosive which he himself had perfected. He shuddered at the thought of the havoc which its detonation would cause.

"Yes, Doctor, that is a can of radite," said the Russian. "Allow me also to call your attention to the interrupter fuse which is attached to it. When Mr. Carnes cuts the wire outside, you know well enough what will happen. Now, let me invite your attention to the clock on the wall before you. Mr. Carnes arrived at the Bush River station of the P. B. and W. at 2:15 A.M. He had a little trouble getting a boat, but he is now on his way here. It is 2:25. I think he will arrive between 3:30 and 4:00. Perhaps five minutes later, he will find the wire.

"You have a little over an hour in which to contemplate your total extinction, an extinction which will remove from my path the one great obstacle to my domination of the world. I hope you will enjoy your remaining moments. In order to help you to enjoy them, and to realize the futility of human endeavor, I have placed the key of your shackles on the floor here in plain sight, but, alas, out of your reach. I would like to stay and watch your struggle, to see the self-control on which you pride yourself vanish, and to watch you whimper and pray for the mercy you would not find; but I am deprived of that pleasure. I must take personal charge of my men to be sure that there is no slip.

Good-by, Doctor, we will never meet again, I fear."

"We will meet again, Saranoff," said Dr. Bird in even tones of cold ferocity which made even Saranoff shiver. "We will meet again, and when you whimper and beg for mercy, remember this moment!"

The Russian started forward with an oath, his hand raised to strike.

He recovered himself and essayed a sickly smile.

"I will remember, Doctor," he said in a voice which, despite himself, had a tremor of fear in it. "I will remember--_when_ we meet again."

He ran lightly up the stairs and Dr. Bird heard the floor close above him. With a grunt, he bent down and examined his shackles closely.

They were tight fitting and made of hardened steel. A cursory examination showed the doctor that he could neither force them nor slip them. He turned his attention to the key which Saranoff had pointed out. It lay on the floor, about ten feet, as nearly as he could judge, from where he stood.

He knelt and then stretched himself out at full length on the floor.

By straining to the uttermost, his groping fingers were still six inches from the key. Saranoff had calculated the distance well.

Convinced that he could not reach the key by any effort of stretching, Dr. Bird wasted none of his precious time in vain regrets or in useless efforts to accomplish the impossible. He rose to his feet and calmly took stock of the room, searching for other means of freeing himself. The shackles themselves offered no hope. He searched his pockets. The search yielded a pocket knife, a bunch of keys, a flashlight, a handkerchief, a handful of loose change, and a wallet.

He examined the miscellany thoughtfully.

A light broke over his face. He tied one end of the handkerchief to the knife and again took a p.r.o.ne position on the floor. Cautiously he tossed the knife out before him. It fell to one side of the key. He drew it back and tried again. The knife fell beyond the key. Slowly he drew it back toward him by the handkerchief. When it reached his hand, he saw to his joy, that the key was a good inch nearer. With a lighter heart, he tried again.

His toss was good. The knife fell over the key, and again he drew it to him. To his disgust, the key had not moved. Again and again he tried it, but the knife slid over the key without moving it. He looked more carefully and saw that the key was caught on an obstruction in the flooring.

With careful aim, he threw his knife so as to drive the key further away. He threw the knife again and tried to draw the key to him from its new position. It came readily until it reached the inequality in the floor which had stopped it the first time. All of his efforts to draw it nearer were fruitless. He give vent to a muttered oath as he looked at the clock. Thirty minutes of his time had gone.

A second time he knocked the key away and strove to draw it to him with no success. The clock bore witness to the fact that another ten minutes had been wasted. He rose to his feet and carefully surveyed his surroundings.

A cry of joy burst from his lips. On the floor was a tiny metallic thread which he knew for a wire. He bent down and picked it up. It was fine and very flexible. He doubled it three times and strove to bend a hook in it. The wire was too short to offer much hope, but he threw himself p.r.o.ne and began to fish for the key.

The wire reached it readily enough, but it did not have rigidity enough to pull the key over the little b.u.mp which held it. A glance at the clock threw him into an agony of despair. A full hour had pa.s.sed since Saranoff had left him. Carnes might even now be walking into the trap which had been laid for him.

He rose to his feet and thought rapidly, twisting the wire idly around the knife as he did so. He glanced at the work of his hands, and an oath broke from his lip.

"Fool!" he exclaimed. "I deserve to die! The means for liberation were in my hands all the time."

With feverish activity, he ripped open the flashlight. He held the two ends of the wire against the terminals of the light battery and touched the knife to his steel key ring. To his joy, the ring adhered to the knife. Under the influence of the battery, the wire-wrapped knife had become a small electromagnet.

In a moment the doctor was p.r.o.ne on the floor. He tossed the knife out to the key. His aim was good and it fell directly beyond. With trembling hands he drew the knife toward him. It reached the key.

Scarcely daring to breathe, he pulled it closer. The key had risen over the ridge which had held it, and was adhering to the knife. In another moment, he stood erect, freed from the shackles which had bound him.

He made for the door at a run, but a sudden thought stopped him. The clock showed him that an hour and twenty minutes had pa.s.sed.

"Carnes must be nearly here!" he cried. "If I go blundering out, I'm liable to run right into the trap they have laid for him, and then we're both gone. If I yell to warn him, the fool will come ahead at full tilt. What the d.i.c.kens can I do?"

His gaze fell on the can of radite. The wires leading to the interrupter fuse gleamed a dull gold with a malign significance.

"If Carnes and I are both washed out, there will be only Thelma left.

She can't fight Saranoff alone. Carnes knows the man and his methods.

There is only one way that I can see to warn him out of the trap."

He shuddered a moment. With a steady step he walked across the cave to the can of deadly explosive. A pair of pliers lay on a nearby bench.

He picked them up. He dashed his hand across his face for a moment, but looked up with steady eyes. With hands that did not tremble, he bent down over the can. With a quick snip, he severed the wires leading to the can of radite.

Operative Carnes jumped ash.o.r.e as the boat reached the bank of Bush River. Before him stretched a dismal swamp, interspersed with occasional bits of higher ground. He looked back over the river for a moment, taking his bearings with great care. A luminous lensatic compa.s.s gave him the orientation of the points he had chosen for markers.

"Are you sure we are at the right place?" he asked in an undertone.

"Sure as shootin', Mister," replied the boatman. "It's the only place of its kind in five miles. The rock you're hunting for is about a hundred rods due east."

"It looks right," said Carnes. "Come on, men."

Operatives Haggerty and Dillon scrambled out of the boat and stood by his side.

"Follow me," said Carnes in a whisper.

Both detectives nodded silently. They drew their pistols and fell in behind their leader. Keeping his direction with the aid of his compa.s.s, Carnes led the way forward, counting his steps. At five hundred he paused.

"It should be right here," he whispered.

Haggerty pointed in silence. In the starlight, a large rock loomed up a few yards away. With an exclamation of satisfaction, Carnes led the way to it.

"Dig on the south side," he whispered, "and hurry! The d.a.m.ned thing is due to go off in less than twenty minutes. Unless we can find and cut the wire before then, the doctor is a gone gosling."