Carnes glanced at the windows and gave a cry of surprise. The gla.s.s was opaque, as had been the gla.s.s in the doctor's laboratory and the gla.s.s in the infirmary at Atlanta. The fogging however, was much more p.r.o.nounced, and the opaque gla.s.s gave faintly the same red effulgence which came from the three bodies.

"What does it mean, Doctor?" he asked.

"I don't know, Carnes," said Dr. Bird slowly. "I foresee that I am going to have to do a great deal of work on short wave-lengths soon.

It is doubtless the effect of some modification of the black lamp which has done it. Look out!"

He leaped to one side as he spoke, drawing Bolton and Carnes with him.

A panel in the side of the wall opposite the doorway had slid silently open and through the opening poured out a beam of fiery red. Full on the three bodies it fell, and then spread out to fill the room. Dr.

Bird had drawn the two nearest men out of the direct beam, but one of the secret service men stood full in its path. In the excitement of entering he had dropped his vitrilene shield and the livid ray fell full on his defenceless body. As they watched an expression of horror spread over his face and he strove to move to one side, but he was held helpless. Slowly he stiffened; and, as the ray bored through him, his body became semi-transparent and the same dull red glow which emanated from the three bodies they had found began to shine forth from him. Bolton strove to break from the doctor's grasp and rush to the rescue but Dr. Bird held him with a grip of iron.

"Too late," he said grimly. "Chalk up another murder to the arch fiend who has committed the others. I don't know the nature of that ray and vitrilene may not be an adequate defence against its full force. We had better get out of here and attack the place from the rear."

Carefully edging their way around the sides of the room, the five men made their way out through the door. Dr. Bird slammed the door shut behind him and led the way out of the building and around to the rear. A door loomed before them and he cautiously tried it. It gave to his touch and he entered. As he set his foot on the threshold a terrific explosion came from the interior of the building.

"Run!" he shouted as he led the way in retreat. "If that is a radite explosion it will act for several seconds!"

From a safe distance they watched. One corner of the building had been torn off by the force of the explosion, and as they watched the rest of the building gradually collapsed and sank into a pile of ruins.

"They had planned on a visit from us all right," said Dr. Bolton grimly. "They had a surprise for us any way we jumped. If we went in the front door, that devil's ray was to finish us, and if we went in the back door the whole place was arranged to blow up as we entered. I only hope that Stanesky thinks that he has got us all and doesn't expect an attack on his next base in the morning. If he doesn't, I think we may give him a rather unpleasant surprise. Of course, that lamp is smashed into atoms and buried under the debris, but I don't know what other devil's contraptions that ruin holds. Bolton, have your men picket it and allow no one near until I get back. I've got to get to a telephone and get a couple of tanks from Meade and a plane or two from Langley Field."

Two tanks made their way slowly across country. The front of each tank was protected by a heavy sheet of vitrilene, while from the turrets of the tanks projected the wicked looking muzzles of thirty-seven millimeter guns. Overhead two airplanes from Langley Field soared, scouting the country. Dr. Bird and Carnes rode in the leading tank.

"It ought to be somewhere near here, unless Karuska lied," said Carnes as he swept the country with a pair of binoculars.

"He didn't lie," returned Dr. Bird. "It was his subconscious mind that spoke and it never lies. He spoke of the gun emplacement as being in a swamp and I have a strong idea that it is submersible. Of course, it is bound to be well camouflaged, both from land and from air observation."

The planes circled around again and again, quartering the air like a pair of well-trained bird dogs will quarter a hunting field. First high and then low they swooped back and forth, the tanks lumbering slowly along in the same direction. Presently the occupants of the leading tank saw one of the planes bank sharply and swing around. It dropped to an alt.i.tude of only a few hundred feet and turned and went back over the ground it had just crossed.

"I believe that fellow sees something!" exclaimed Carnes.

As he spoke, three green Very lights came from the c.o.c.kpit of the plane. The tank driver gave a grunt of satisfaction and turned the nose of his vehicle in that direction. The second tank followed.

Hardly had they turned in the new direction before the ground began to get soft under their tracks and the heavy vehicles began to sink. The driver of the Doctor's tank forced it ahead, but the tank sank deeper in the mire until water flowed in around the feet of the occupants.

"I reckon we'll have to get out and walk pretty soon, Doctor," said the driver.

Dr. Bird grunted in acquiescence. The tank made its way forward a few yards before the engine sputtered and died. The second tank stopped when the first one did, fifty yards behind it. Donning vitrilene helmets and taking vitrilene shields in their hands, the crews of both tanks climbed out into the waist-deep water and gathered around the Doctor for orders.

"Form a skirmish line at ten-pace intervals and cross the swamp," he directed. "We may meet with no opposition, but if there is, the more scattered we are, the safer we will be. You all have hand grenades as well as your rifles?"

A murmur of a.s.sent answered him and the line formed and started across the swamp. They had gone perhaps a hundred yards when three red lights came from one of the planes circling overhead.

"Down!" cried the doctor, dropping to his knees in the muck.

Four hundred yards ahead of them a concrete platform emerged from the marsh and rose slowly into the air. It was roofed with a dome of what looked like plate gla.s.s, but which the doctor shrewdly suspected was vitrilene. When the base of the platform was two-feet above the level of the water the dome slid silently aside disclosing two men bending over a tiny gun. Dr. Bird leveled his binoculars.

"That's the Breslau gun model that was stolen as sure as I'm a foot high!" he cried. "They must have made some miniature sh.e.l.ls and be planning to fire it."

Slowly a pall of intense blackness rose from the marsh and enveloped the platform and hid it from view. A whining noise came from overhead, and then a crash like a thunderbolt. The blast of the explosion threw the attackers face down in the swamp, and when they arose and looked back there was merely a gaping hole where the leading tank had been.

The second tank suddenly seemed to rise in the air and fly into millions of tiny fragments, and a second thunderous blast sent them again to their knees.

"Radite!" bellowed Dr. Bird to Carnes. "Imagine the effect if that had been a full charge fired from a completed Breslau gun! Watch the planes, now. I think they are going to drop a few eggs on them."

The black mist cleared as if by magic and the platform was in plain view. The big gla.s.s dome rolled back into place as the two planes swept over at an elevation of two thousand feet. From each one a small black cigar-shaped object was released and fell in a long parabola toward the earth. The gla.s.s dome which had been closing over the gun platform rolled quickly back and a long beam of intense blackness pierced the heavens. First one and then the other of the falling bombs disappeared from view into it, and then the black column faded from view. The two bombs fell with increasing speed but the dome closed over the platform before they struck. The two hit the dome at almost the same instant and instead of the blinding crash they expected, the watchers saw the bombs rebound from the dome and fall harmlessly into the water.

"Stymied!" muttered the doctor. "I wonder what other properties that confounded lamp has."

He resumed his advance, Carnes and the soldiers keeping abreast of him. When they were within two hundred yards of the platform it rose again and the transparent dome rolled back. A beam of black shot forth over the swamp, searching them out and hiding them from view. First one and then another felt the effects of the black beam; but the vitrilene which the Doctor had provided stood them in good stead, and, aside from a slight shortening of their breath, none of the attackers felt any the worse.

"Come on, men!" cried the Doctor as his athletic figure plowed forward through the breast-deep water. "That is their worst weapon and it is harmless against us!"

Cheering, they fought their way toward the platform. It sunk for a moment and then rose again. As the dome swung back a sharp crackle of machine-gun fire sounded and the water before them was whipped into foam by the plunging bullets. One of the soldiers gave a sharp cry and slumped forward into the water.

"Fire at will!" shouted the lieutenant in command.

A crackle of rifle fire answered the tattoo of the machine-gun, and the sharp ping of bullets striking on the dome could be plainly heard.

An occasional shot kicked up a spurt of white dust from the concrete, but the machine-gun kept up a steady rattle of fire and the soldiers kept their heads almost at the level of the water. There came the roar of an airplane motor, and one of the planes swept over the platform, a hundred yards in the air, with two machine-guns spraying streams of bullets onto the platform. Two men abandoned their machine-gun and crouched under the partially folded-back dome as the second plane swept over, and Dr. Bird took advantage of the lull to advance his party a few yards nearer. Again the defenders of the platform rushed to their gun, but the first plane had turned and swooped down with both guns going, and again they were forced to take shelter while the Doctor and his force made another advance.

The second plane had turned and followed the first, but the defenders had had enough. The transparent dome closed over them and the platform sank into the marsh. With a shout, Dr. Bird led the way forward again.

The attackers were within a hundred yards of the platform when it again rose above the surface of the water. The guns had disappeared, but in their place stood an airship. It was a small affair with stubby wings above which were two helicopter blades revolving at high speed.

No sound of a motor could be heard.

The transparent dome rolled back and like a bullet the little craft shot into the air, followed by a futile volley from the soldiers.

Hardly had it appeared than the two airplanes bore down on it with machine-guns going. The helicopter paid no attention to them for a moment, and then came a puff of smoke from its side. The leading plane swerved sharply and the helicopter fired again. The leading plane maneuvered about, trying to get a machine-gun to bear, while the second plane climbed swiftly to get above the helicopter and pour a deadly stream of fire down into it. It gained position and swooped down to the attack, but another puff of smoke came from the side of the helicopter and there was a thunderous report and a blinding flash in the sky. As the smoke cleared away, no trace of the ill-fated plane could be seen. The helicopter hung motionless in the air as though daring the remaining plane to attack.

The plane accepted the challenge and bore down at full speed on the stranger. Again came a puff of smoke, but the plane swerved and an answering shot came from its side. It was above the helicopter, and the sh.e.l.l which missed its mark plunged to the ground. When it struck there came a roar and a flash and the whole earth seemed to shake. The helicopter shot upward into the air and forward, both its elevating fans and its propellers whirling blurs of light. The airplane followed at its sharpest climbing angle, but was helpless to compete with its swifter climbing rival.

"He's got away!" groaned Carnes.

"Not yet, old dear!" cried the Doctor hopping with excitement. "He isn't safe yet. I never told you, but one Breslau gun had been made and it is on that plane. It has deadly accuracy and is good for fifteen miles. That's Lieutenant Dreen at the controls and Mason at the gun."

As he spoke the plane swung around and made a half loop. For a few yards it flew upside down and then whirled swiftly. As it turned there came a sharp report and a puff of smoke from its rear c.o.c.kpit. High above, the helicopter had ceased climbing and hovered motionless. As the plane fired, the helicopter shot forward like an arrow from a bow, and thereby spelled its doom. Not for nothing did Captain Mason bear the t.i.tle of the best aerial gunner in the Air Corps. He had foreseen what the action of his opponent would be and had allowed for just such a move. Far up in the sky came a blinding flash and a cloud of smoke.

When the smoke cleared the sky was empty, except for a little scattered debris falling slowly to the ground.