The two detectives drew intrenching shovels from their pockets and dug feverishly. For five minutes they labored. Dillon gave an exclamation.

"Here it is, Chief!" he said.

Carnes bent down and ventured a short flash from a carefully guarded light. The detective's shovel had unearthed a powerful cable running through the earth.

"Get something to cut on!" cried Carnes.

Haggerty lifted a rock which they had unearthed and thrown to one side. Carnes raised the cable and laid it on the rock.

"Now for your ax, Dillon!" he exclaimed.

He turned on his flashlight. Dillon raised a hand-ax and took careful aim. Sparks flew as the ax fell on the rock, severing the cable cleanly. Carnes rose to his feet.

"The doctor's safe!" he cried.

He started at a run toward the north. He had gone only a few feet when a beam of light flashed across the marsh, picking him out of the darkness. He paused in amazement.

A flash of orange light stabbed the darkness and a heavy pistol bullet sang past his head. The detective raised his weapon to reply, but three more flashes from the darkness were followed by the vicious cracks of large caliber automatics.

"Down, Chief!" cried Haggerty.

Carnes dropped to the ground, the beam of light following his movements. Four more flashes came from the darkness. Mud was thrown up into his face. Dillon's gun joined Haggerty's in barking defiance into the night.

A groan came from Haggerty.

"Hit, Tom?" asked Carnes anxiously.

"A little, but don't let that bother you. Get that d.a.m.ned light!"

He fired again, groaning at he did so. There was a crash from over the marsh and the light went out.

"Good work, Tom!" cried Carnes.

He raised his pistol and fired again and again into the darkness, from which still came the flashes of orange light. A cry of pain rewarded him.

"Come on, men, rush them!" he cried.

He jumped to his feet and dashed forward. A fresh beam of light stabbed a path through the darkness. A volley of fire came from behind it. Haggerty stumbled and fell.

"They've got me, Chief!" he cried faintly.

Disregarding the storm of bullets, Carnes charged ahead, Dillon at his heels. A sudden shout came from his left. A fresh beam of light made a path through the darkness and Carnes could see his opponents lying p.r.o.ne on the marsh. A cry of dismay came from them. Carnes fired again as he rushed forward. The men leaped to their feet and fled away into the darkness.

"Your light, Dillon!" he cried.

Dillon's light shone out and picked up one of the fleeing figures. The beam from the left was centered on another.

"Halt!" came a stern voice from behind the light. "You are surrounded!

If I give the word to fire, you are dead men!"

"Dr. Bird!" cried Carnes in amazement.

The fleeing man in the beam of Dillon's light paused.

"Drop your gun!" cried Carnes sharply.

There was a moment of hesitation before the man's gun fell and his hands went up.

"Get him, Carnes!" came Dr. Bird's voice. "I've got another one held out here. I hope one of them is the man we want."

As Dillon slipped handcuffs on his prisoner, Dr. Bird came forward, driving another Russian before him. In his hand was a piece of iron pipe.

"Cuff him, Carnes!" he said.

The detective slipped handcuffs on the man while Dr. Bird bent down and examined the face of each of the prisoners with his light. He straightened up with an exclamation of anger.

"These are nothing but tools," he said bitterly. "We had the arch-conspirator himself in our hands and let him escape."

"The arch-conspirator!" gasped Carnes. "You don't mean Saranoff?"

"Yes, Ivan Saranoff. He was here on this marsh to-night. There were four of his men and we got two, letting the most important one get away."

"You've got four, Dr. Bird," said a guttural voice from the dark.

Dr. Bird whirled around and shot out the beam of his light. A third Russian was revealed in its gleam.

"Hands up!" cried the doctor.

"I'm willing to be captured, Doctor," said the Russian. "Your search for Saranoff is useless. He has been gone for an hour. He is not one to risk his own skin when others will risk theirs for him. He fled after he left the cave."

"Do you know where he has gone?"

"I wish I did, Doctor. If I knew, we'd soon have him, I hope."

The Russian's voice had changed entirely. Gone were the heavy guttural tones. In their place was a rich, rather throaty contralto. Carnes gave a cry of astonishment and turned his light on the prisoner.

"Thelma!" he gasped.

The Russian smiled.

"Surely, Mr. Carnes," she said. "Congratulations on your ac.u.men. Dr.

Bird saw me for half an hour this evening, but he didn't recognize me.

He even knocked me out with his fist back in the cavern."