The creature crouched lower, with its legs twitching in obvious preparation for a spring. Dixon looked wildly about him for a possible weapon, but saw nothing. Then he suddenly remembered the little lead grenade in his pocket. The cataclysmic power of that little bomb should be more than a match for even this monster.

His fingers closed over the grenade just as the great spider's twitching legs straightened in a mighty effort that sent it hurtling through the air straight toward him.

Dixon dodged to one side with a swiftness that caused the monster to miss by a good yard. Dixon raced a dozen paces farther away, then whirled to face the great spider. The creature's legs began scuttling warily forward. It was to be no wild leap through the air this time, but a swift rush over the ground that Dixon would be powerless to evade.

Releasing the safety catch of the grenade, Dixon hurled the tiny missile straight at the rock floor just under the feet of that vast misshapen creature. There was a vivid flash of blinding blue flame, then a terrific report. Dazed by the concussion, but unhurt, Dixon cautiously went over to investigate the result of the explosion.

One brief glance was enough. The hideous ma.s.s of shattered flesh sprawling there on the rocks would never again be a menace. The only thing that had escaped destruction in that shattering blast was the strange head-piece the thing had worn. Either the small shining globe was practically indestructible, or else it had been spared by some odd freak of the explosive, for it still blazed in baleful opalescence atop the shattered head.

Dixon hurried back to where Emil Crawford and Ruth Lawton lay. The girl's body was so rigidly inert that Dixon threw back his enc.u.mbering hood and knelt over her for a swift examination. His fears were quickly realized. Ruth was already a victim of the green moon's dread paralysis.

"Dixon! Bruce Dixon!"

Dixon turned at the call. Emil Crawford, his face drawn with pain, had struggled up on one elbow. The old man was obviously fighting off complete collapse by sheer will power.

"Dixon! Replace Ruth's shining head-piece at once!" Crawford gasped.

"That will make her immune from the Green Death, and then we can--"

The old man's voice swiftly faded away into silence as he again fainted.

Dixon hurriedly searched the scene and found Ruth's head-piece on the ground where it had apparently fallen in her first struggle with the giant spider, but the tiny white globe in the device was shattered and dark.

Despair gripped Dixon for a moment. Then he remembered the unbroken head-piece of the slain monster. True, the glow of its globe was opalescent instead of white, but it seemed to offer its wearer the same immunity to the green moon's rays.

He swiftly retrieved the head-piece from the spider-creature's body, and set the light metal framework in place on Ruth's auburn curls.

Results came with incredible quickness. The rigidity left Ruth's body immediately. Her breath came in fast-quickening gasps, and her eyes fluttered open as Dixon knelt over her.

"It's Bruce, Ruth--Bruce Dixon," he said tenderly. "Don't you know me, dear?"

But there was no trace of recognition in those wide-open blue eyes staring fixedly up at him. For a moment Ruth lay there with muscles strangely tense. Then with a lithe strength that was amazing she suddenly twisted free of the clasp of Dixon's arms and sprang to her feet.

The next minute Dixon gave ground, and he found himself battling for his very life. This was not the Ruth Lawton whom he had known and loved. This was a madwoman of savage menace, with soft lips writhing over white teeth in a jungle snarl, and blue eyes that fairly glittered with unrestrained, insensate hate.

He tried to close with the maddened girl, but instantly regretted his rashness. Her slender body seemed imbued with the strength of a tigress as she sent slim fingers clawing at his throat. He tore himself free just in time. Dazed and shaken, he again gave ground before the fury of the girl's attack.

He could not bring himself to the point of actively fighting back, yet he knew that in another moment he would either have to mercilessly batter his beautiful adversary into helplessness or else be himself overcome. There was no middle course.

Then old Emil Crawford's voice came again as the old man rallied to consciousness for another brief moment.

"Bruce, the opal globe is a direct link to those devils themselves!

Break it, Bruce, break it--for Ruth's sake as well as your own!"

Crawford had barely finished his gasped warning when Ruth again hurled herself forward upon Dixon with tapering fingers curved like talons as they sought his throat. Dixon swept her clutching hands aside with a desperate left-handed parry, then s.n.a.t.c.hed wildly at the gleaming head-piece with his right hand.

The thing came away in his grasp, and in the same swift movement he savagely smashed it against the rocky wall beside him. Whatever the opalescent globe's eery powers might be, it was not indestructible. It shattered like a bursting bubble, its fire dying in a tiny cloud of particles that shimmered faintly for a moment, then was gone.

Again, the effect upon Ruth was almost instantaneous. Every trace of her insane fury vanished. She swayed dizzily and would have fallen had not Dixon caught her in his arms. For a moment she looked up into his face with eyes in which recognition now shone unmistakably. Then her eyelids slowly closed, and she again lapsed into unconsciousness.

Dixon looked over at Emil Crawford, and found that the old man had again collapsed. Dixon knew of but one thing to do with the stricken man and girl, and that was to take them to his laboratory. The laboratory, apparently insulated by veins of lead ore in the mountain surrounding it, was the one sure spot of refuge in this weird nightmare world of paralyzing lunar rays and prowling monsters.

Flinging his tunic over Ruth's head to shield her as much as possible from the moonlight, he carried her to the laboratory, then returned for Emil Crawford. Safe within the subterranean retreat with the old scientist, Dixon removed his enc.u.mbering lead costume and began doing what he could for the stricken pair.

Ruth was still unconscious, but the cataleptic rigidity was already nearly gone from her body, and her breathing was now the deep respiration of normal sleep.

Emil Crawford's condition was more serious. Not only was the old man's frail strength nearly exhausted, but he was also badly wounded. His thin chest was seared by two great livid areas of burned flesh, the nature of which puzzled Dixon as he began to dress the injuries. They seemed of radioactive origin, yet in many ways they were unlike any radium burns that Dixon had ever seen.

While Dixon was working over him, Crawford stirred weakly and opened his eyes. He sighed in relief as he recognized his surroundings.

"Good boy, Bruce!" he commended wanly. "We are safe here among the insulating veins of lead ore in the mountain. This is where Ruth and I were trying to come after we escaped from those devils to-night. But, Bruce, how did you guess the radioactive nature of the Green Sickness in time to avoid falling a victim to it as soon as you left the shelter of your laboratory?"

"My escape was entirely luck," Dixon admitted grimly. "To-night I left my laboratory for the first time in three days. I found a world gone mad, with a strange green moon blazing down upon a land of living dead men, and with marauding monsters hideous enough to have been sp.a.w.ned in the Pit itself. What in Heaven's name does it all mean?"

"I am afraid that it means the end of the world, Bruce," Crawford answered quietly. "It was a little over forty-eight hours ago that the incredible event first happened. Without a moment's warning, _the moon turned green_! Hardly had the world's astronomers had time to speculate upon this amazing phenomenon before the Green Sickness struck--a pestilence of appalling deadliness that swept resistlessly in the path of those weird green rays. Wherever the green moon shone, every living creature succ.u.mbed with ghastly swiftness to the condition of living death that you have seen.

"Westward with the racing moon sped the Green Sickness, and nothing stayed its attack. The green rays pierced through buildings of wood, stone, and iron as though they did not exist. A doomed world had neither time nor opportunity to guess that lead was the one armor against those dread rays. To-night, Bruce, we are in all probability the only three human beings on this planet who are not slumbering in the paralytic stupor of the Green Sickness.

"Ruth and I were stricken with the rest of the world," Crawford continued. "We recovered consciousness hours later to find ourselves captives in the Earth-camp of the invaders themselves. You probably saw the display of lights that marks their camp down in the valley a mile beyond my place. We have learned since that the s.p.a.ce ship of the invaders dropped silently down into the valley the night before the moon turned green and established the camp as a sort of outpost and observatory. They left two of their number there as pioneers, then the rest of them departed in the s.p.a.ce ship for their present post up near the moon.

"Ruth and I were revived only that the two invaders in the camp might question us regarding life on this planet. They have a science that is based upon principles as utterly strange and incomprehensible to us as ours probably is to them. They probed my brain with a thought machine.

It was an apparatus that worked both ways. What knowledge they got from me I do not know, but I do know that they unwittingly told me much in the bizarre and incredible mental pictures that the machine carried from their brains to mine.

"They are refugees. Bruce, from a planet that circled about the star that we know as Alpha Centauri, a star that is the nearest of all our stellar neighbors, being only four and a third light years distant.

Their home planet was disrupted by a colossal engineering experiment of the Centaurians themselves, the only survivors being a group of fifty who escaped in a s.p.a.ce ship just before the catastrophe.

"There were no other habitable planets in their own system, so in desperation these refugees sped out across the void to our solar system in the hope of finding a new home here. They reconnoitered our Earth secretly and found it ideal. But first they believed that they must conquer the life that already held this Earth. To do this, they struck with the Green Sickness.

"The rays that are turning the moon green emanate from the s.p.a.ce ship hovering up there some fifty thousand miles from the moon itself. The Centaurian's rays, blending with the sunlight striking the disc of the full moon, are intensified in some unknown way, then reflected across the quarter of a million miles to the Earth, to flood this planet with virulent radiance.

"The green moonlight is radioactive in nature, and overcomes animal life within a matter of fifteen minutes or less. The rays are most powerful when the moon is in the sky, but their effect continues even after it has set, because as long as the green moonlight strikes any part of the Earth's atmosphere the entire atmospheric envelope of the planet remains charged with the paralyzing radioactive influence.

"Earth's inhabitants are not dead. They are merely stupefied. If the green rays were to cease now, most of the victims of the Green Sickness would quickly recover with little permanent injury. But, Bruce, if that evil green moon blazes on for twenty-four hours more, the brain powers of Earth's millions will be forever shattered. So weakened will they be by then that recovery will be impossible even with the rays shut off, and the entire planet will be populated only by mindless imbeciles, readily available material for the myriads of monstrous hybrids that the invaders will create to serve them.

"To-night you saw the hybrid that the invaders sent to recapture Ruth and me. It was a fit specimen of the grisly magic which those devils from outer s.p.a.ce work with their uncanny surgery and growth-stimulating radioactive rays. The basic element of that monster was an ordinary tarantula spider, with its growth incredibly increased in a few short hours of intensive ray treatment in the Centaurian's camp. The half-head grafted to it was that of a human being. They always graft the brain cavity of a mammal to a hybrid--half heads of burros, horses, or even dogs, but preferably those of human beings. I think that they prefer to use as great a brain power as possible.

"The hybrids are controlled through the small opalescent globes on their heads, globes that are in direct tune with a huge master globe of opalescent fire in the invaders' camp. When Ruth attacked you after you placed the opal head-piece upon her head, she was for the moment merely another of the invaders' servants blindly obeying the broadcast command to kill. The white globes that Ruth and I wore when we escaped from the camp were identical with those worn by the invaders themselves, being nothing more than harmless insulators against the effect of the green moonlight."