Part 1

INVADERS OF THE FORBIDDEN MOON

By RAYMOND Z. GALLUN

Annihilation was the lot of those who ventured too close to the Forbidden Moon. Harwich knew the suicidal odds when he blasted from Jupiter to solve the mighty riddle of that cosmic death-trap.

[Transcriber's Note: This etext was produced from Planet Stories Summer 1941. Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed.]

"Calling the pilot of space ship X911!" Evan Harwich shouted into the radio transmitter of his little Interplanetary Patrol Boat. "Good God! Turn your crate back, you crazy fool! Don't you know you're headed right into the danger zone of Jupiter's Forbidden Moon? You'll get yourself burned to a crisp in another few seconds if you don't turn back...."

Evan Harwich's growling voice was almost shrill at the end. His police duties patrolling the vicinity of Io, innermost of Jupiter's larger satellites, rarely developed moments as tense as this. Most other pilots had brains enough to give the Forbidden Moon a wide berth. And for excellent if mysterious reasons!

Yet the craft ahead, a sleek new job with the identification number X911 painted on its conning tower, kept steadily on. Its slim hull, which betrayed an experimental look, was pointed straight at the threatening greyish disc of Io, the one world in the solar system which no exploring ship of the void had ever reached--intact!

Almost everybody among the inhabited spheres knew about the dangers of the desolate Forbidden Moon. Ever since the colonial empire of Earth had been extended to the region of Jupiter and his numerous satellites, Io had been a grim menace; sure destruction to any rocket that approached within five thousand miles of its dreary, almost airless surface.

Nobody seemed to know just why this was true; but some scientists claimed that somehow there was an invisible layer or shell all around Io; an immense blanket of strange energy or force that fused and blasted the metal hulls of all ether craft that ran into its insidious web.

Tensely and helplessly Evan Harwich watched, as the ship ahead continued on its way toward what seemed sure catastrophe. No danger in front of the recklessly piloted craft could be seen, of course. Five thousand miles of clear, cold vacuum was all that was visible between it and Io. But since this region held concealed in it all the potential violence of a hair-triggered trap, ready to unleash a flaming death that involved unknown physical laws and principles, maybe it wasn't just plain vacuum after all!

With dogged persistence Harwich kept yelling futile warnings into his radio. His shouts and curses were unheeded, and no answer was given. He knew what was going to happen in another second. There would be a burst of dazzling white fire all around the rocket of this foolhardy pilot he had tried to save from suicide. Metal would drip and sparkle in the absolute zero of space. In just another instant....

Harwich swung his patrol boat aside, not caring to end his own life. But he kept watching the X911 from the side-ports of his cabin.

And now, something quite different from what he had expected was taking place. Suddenly the apparently doomed ship was enveloped in a bluish halo which seemed to emanate from a great helix or spiral of metal that wrapped its hull!

Immediately afterward, as the X911 entered definitely into the zone of destruction around Io, great white sparks lanced dazzlingly through the blue halo. It was as though the latter was fighting back those gigantic, unknown forces that had seemed to make the Forbidden Moon forever inviolable. It was as though the halo was keeping the X911, and whoever was flying it, safe!

Evan Harwich's slitted eyes widened a little in astonishment and hope. "Dammit!" he grumbled happily. "That idiot's got some kind of new invention that's protecting him! Maybe the Forbidden Moon is going to be reached and explored after all!"

A second more that weird conflict of hidden forces continued. Watching it was like watching a race, on which you have staked everything you own. Visibly, that daredevil space ship seemed to slow, as if resisted by a tangible medium. For an agonizing instant of suspense, Harwich saw those wicked sparks brighten in the X911's bluish aura. Then the latter dimmed, flickered, went out!

As if angry demons were waiting to pounce, destruction struck--quicker than a lightning bolt.

* * * * *

If there had been any humor in the situation before, it was gone now utterly! The patrol man's lips dropped apart in sheer awe. The muscles of his massive, freckle-smeared forearms tightened futilely as he longed to help the X911's doomed pilot. In the pit of his stomach there was a sickish feeling.

Where that rocket that had dared the inscrutable enigma of the Forbidden Moon had been, there was a sudden, terrific blaze of light. The intolerable incandescence of it seemed to reach out to infinity itself, illuminating even the blackness between the distant stars of space. But it was all as silent as the bouncing of a bubble on velvet. No explosion, however huge, can transmit sound in the emptiness of the void.

The magnificent, horrible blast broke into a million gobs and sparks of molten metal--from what had once been a space ship's hull. Superheated gas from ignited rocket fuel shot out. Scattered far and wide, the white-hot fragments of the wreck continued on their way, following the original direction of the once bold X911 toward Io. Their speed increased gradually, as the gravity of the Forbidden Moon pulled them. The larger chunks, falling at meteoric speed, would bury themselves deep in the cold Ionian deserts.

The secret of Io had claimed another victim, one who might have been victorious. But Io's mystery was still unviolated. Evan Harwich had seen other ships, disabled and unmaneuverable for some reason beforehand, go to their ends like this; but he was still not used to the spectacle, and to the unholy wonder it provoked in him.

Dazzled and almost blinded, he guided his patrol boat shakily away from the Forbidden Moon. There was cold sweat in his thick, black hair, under his leather helmet; and cold sweat too on his narrow, bristly cheeks. His movements of the controls were a trifle vague and fumbling with emotion, making his patrol boat waver a little in its course.

For perhaps the millionth time Harwich wondered: "What makes Io so dangerous? Dammit all, those scientists who claim that there is a deadly shell of unseen energy completely enveloping the Forbidden Moon, must be right! There isn't anything else that could explain the continual destruction of all rocket craft that come within that five-thousand-mile limit!"

Evan Harwich was ready to accept this much as fact. But beyond this, there was still a vast, unguessable question mark.

Was this shell of energy a natural phenomenon; or was it something planned, made, intended for a purpose? If the latter guess was right, who could have created such a gigantic screen of force? What kind of beings? What kind of science?

Io was an almost dead world, Harwich knew. Very cold. Very little water and air. Astronomers had taken photographs of its terrain through powerful telescopes, from the other moons of Jupiter. Very little could be seen on those photographs but deserts and grey hills, and curious formations which might be the magnificent ruins left by an extinct race.

Evan Harwich was far from a weakling; but cold chills were playing over his big body as he groped to understand the unknown.

His vision was clearing somewhat, after having been so dazzled by the incandescent blast that had accompanied the destruction of the X911 a moment ago.

In the feeble sunlight, so far out here in the void, Harwich saw a second rocket, leaving the scene of the disaster along with himself. Evidently someone else had witnessed that weird demonstration of Io's destructive might, too!

Squinting through a pair of binoculars, Harwich read the obviously ancient craft's number. Then he snapped on his radio again.

"Calling space ship RQ257!" he grated into the transmitter. "Interplanetary Patrol just behind you. Pilot, please identify yourself! Do you know who was aboard the experimental rocket X911, that was just destroyed?"

A few seconds later he heard a dazed, grief-anguished voice speaking in response: "Yes ... I ought to know. I came out to watch our test of the Energy Barrage Penetrator, which we thought would be successful. I am Paul Arnold. The man who was just killed was John Arnold, my father."

John Arnold! Yes, Harwich had often seen photographs of this daring, hawk-faced old student of the Forbidden Moon in the scientific journals. He had been the greatest of them all! But there wasn't much to do for him now but shrug ironically, and report the nature of his death by radio to the Interplanetary Patrol Base on Ganymede, largest of Jupiter's satellites.

"I'm sorry, Paul Arnold," the patrol man told his informant in sincere sympathy.

"Thank you," the quavering voice of Paul Arnold returned. "And now, if you don't mind, I've got to get back to Ganymede City. Dad's gone, but I've got to carry on his work."

* * * * *

Harwich didn't meet Paul Arnold, the son of the dead scientist, face to face for more than a month, Earthtime. But on patrol duty out there in the lonely reaches of the void, with the stars and the roar of his rocket motors for company, he saw a good deal of the leering, greyish sphere of Io. It seemed to taunt him with its masked secrets, hanging so near to the tremendously greater bulk of Jupiter. But the Forbidden Moon told him nothing new at all. Through his binoculars he saw the deserts and hills and those supposed ruins. Near the equator was something that looked like a vast, pointed tower. But Harwich had seen this before, often. Something moved near the tower now and then, as on other occasions. But maybe this distant movement was only the shifting of clouds of dust, blown by a thin, frigid wind, in a tenuous atmosphere.

Then, back in Ganymede City, came that meeting with Paul Arnold. It happened at the Spacemen's Haven. Evan Harwich, on furlough now, was sipping Martian _kasarki_ at the bar.

Presently a hand was laid on his arm. He turned to face a slight-built youngster, who could not have been more than eightteen. But his peculiar gold-flecked eyes were as distant and scared and bright as if they had seen Hell itself.

"You're Harwich," said the boy. "I'm Arnold. They pointed you out to me as the patrol pilot who reported my father's death. I wanted to talk to you. I don't know just why, except that you were there too, when Dad was killed. You saw what happened. And people have told me that you were a square shooter, Harwich."

Somewhat startled, but glad to know the youth, and more than willing to talk with him on the subject mentioned, Evan Harwich tried to smile encouragingly. It wasn't too easy, considering his weathered, space darkened features and threatening size; but he did his best.

"Pleased to meet yuh, Arnold," he said rather clumsily, offering a big hamlike hand. "I wanted to talk to you too. How about a drink and a quiet corner, where the crowd here won't be stepping all over us?"

They retired to a table in a screened nook. "Now," said young Arnold, "you've seen as much of the Forbidden Moon as anybody alive, Harwich. You must know that the energy aura around her is real and not a fable. You must know, too, that it couldn't be a natural phenomenon, since nothing in nature acts like it does. There's only one alternative possibility as to what could cause it! Even though Io seems so deserted, somehow there are machines there, functioning to maintain that shell of force! Right?"

Harwich nodded. Little glints of intense interest seemed to show in his eyes. "I've believed that for a long time," he admitted. "But those machines must be plenty wonderful to build up a barrage of invisible energy, thousands of miles in extent! Our scientists couldn't even begin to dream of doing anything like it! Even the principles employed must be a million years ahead of our time!"

"Right again!" the boy responded. For a second he cast a guarded, suspicious glance around the room, where Earthmen and leathery Martians were talking and laughing and drinking.

"The evidence can't be disputed," Paul Arnold whispered at last. "It might be that the people who invented those machines have been extinct for ages. But the mechanisms they created are still operating. There's superscience there on Io, Harwich! How much could we benefit civilization, if we could somehow find out what the principles of those machines are? How much damage might be done if those principles happened to fall into the wrong hands, among men? War and conquest--a whole solar system thrown into chaos--might result!"

Evan Harwich wanted to laugh scornfully, wanted to call the kid a dreamer of wild dreams; but the realization that young Arnold probably told the truth, made his hide tingle and pucker instead.

"Maybe you're right, fella," he growled.

"Of course I am!" Arnold almost snapped. "My father believed it for years, and his work must go on, even though the Forbidden Moon scares me plenty. You saw yourself, Harwich, that his Energy Barrage Penetrator was almost successful. I've been trying to build another, with enough power to get through."

Harwich's lips curved, a nameless, wild thrill stirring in his blood. But after all, even before he'd left a great consolidated farm in southern Illinois nine years ago, to become a spaceman, he'd been an adventurer at heart.

"Do you suppose you'll need any help?" he asked simply, realizing that even as he spoke, death on a tomb-world might well be lurking in the background.

The question sounded like impulse, but it wasn't. Harwich had lived too long in the shadow of the Forbidden Moon's taunting enigma, not to want to take a personal part in any effort to penetrate its grim secrets. Besides, he had a month's furlough from patrol duty now. The thought of possible adventures to come made his nerves tingle.

Paul Arnold's eyes widened. "I almost hoped you would want to join me, Harwich," he stammered happily, seeming only to need the moral support of an experienced spaceman, to bring him out of the black mood he was in. "Shall we go to my laboratory?"

* * * * *

The Arnold lab and dwelling proved to be one of the oddest that Evan Harwich had ever seen. It was just outside the great steel-ribbed airdrome that confined a warm, breatheable atmosphere over Ganymede City, the small mining metropolis of a dying world.

The Arnold lab was a group of subterranean rooms, beneath the desert. They were reached by a private tunnel from the City, and were hermetically sealed against leakage of air to the cold semi-vacuum of the Ganymedean atmosphere above.

Cellar rooms, vaults, not exactly modern but restored from some ancient ruin; for Ganymede had had its extinct clans of quasihuman people too, ages ago. A weird place, this was, a place of poverty, perhaps, since all of the Arnold resources must have gone into experimentation; but a homey sort of place, too, with its scatterings of books and quaint art objects and pictures.

"This is the Energy Barrage Penetrator, Harwich," Paul Arnold was saying in husky tones, as the two men bent over a copper helix or spiral, attached to a maze of wires, tubes, and power-packs. "I rebuilt it here on this test-block from Dad's plans; with certain rearrangements, of course. But we need a new Gyon condenser, if we want to raise the Penetrator's strength enough to make our venture successful."

Evan Harwich nodded beneath the single illuminator bulb that glowed here, its rays glinting from the battered, patched hull of the space ship, RQ257, that stood in the center of the great room, under the airtight exit doors provided for it in the ceiling.

"So I see," Harwich commented with subdued eagerness. "Well, that's not so bad. I can buy a new Gyon condenser from one of the supply shops in town. I'm no scientist, fella, but they give us a pretty complete scientific training in the patrol service. Enough so that I can see that the Penetrator is going to do the trick, this time, with your improvements. And I don't think it will take very long to get things ready for a real trip to the Forbidden Moon."

The patrol man had hardly finished speaking, when a door, somewhere, groaned on its hinges. In the dusty silence there were footsteps, coming nearer through the series of rooms.

"Well, have we got company?" a voice boomed heavily after a moment.

Evan Harwich turned about slowly. Standing in the arched entrance of the laboratory chamber, beneath the ancient, grinning gargoyle of carven granite that formed the keystone of the arch, were two people. They must have just come in from town.

One was a man, as tall as Harwich himself, but much broader. He looked jovial, overfed, and just faintly sly. Harwich knew him a little. He kept a small printer's establishment in Ganymede City, repaired delicate instruments, and made loans on the side.

"Hello, Harwich!" the big man greeted loudly. "You look surprised to see me here! Well, I'm just as up in the air as you are, to find you around. How come? You see I've been financing Paul Arnold's researches since old John was killed. Has Paulie talked you into some part in the great miracle hunt on Io, too?"

"Hello yourself, Bayley," the patrol man returned in not too friendly a tone. "Yes, I've joined up."

Harwich was a little more than surprised to see the fat printer here. He didn't like the setup at all. Not that he had anything definite against George Bayley. The latter had always seemed good-natured and honest, except for some elusive trace of insincerity in his manner, his voice, and his little squinted eyes.

Was this the kind of man for Paul Arnold to choose as a patron, particularly when he was in pursuit of the incredibly advanced science which must exist on Io? A science that might benefit the human race immeasurably, or might result in wholesale destruction and confusion, if it was wrongly and selfishly used?

Evan Harwich couldn't have answered yes or no to this question.

* * * * *

There was a painful pause in the conversation. Harwich found himself looking at the girl, who had entered with the big printer, and to whose arms the latter clung with a kind of bearish possessiveness. She was small and dainty. Her blonde hair, combed back tightly, fitted her head like a cap. She was wearing a plain but tasteful black dress with a white collar.

"Oh, I'm sorry!" Paul Arnold exclaimed after a moment. "Clara, this is Evan Harwich of the Patrol. Evan, this is my sister. I didn't tell you that I had a sister, did I?"

The girl only nodded slightly, and smiled a warm, friendly little smile. But why did the big patrol pilot find her more attractive than any other girl he had ever seen? Perhaps mostly it was those wistful eyes of hers, not gold flecked like her brother's, but clouded amber. They were mild and troubled and knowing. Maybe Clara Arnold's life, as the daughter of a martyred scientist, had made them like that. Harwich knew that he might conquer not only the Forbidden Moon, but the stars themselves, and still remember those eyes.

"Now we all know each other," Bayley boomed. "We're one big happy family--or are we?" He looked at Harwich significantly, a definite scowl now crinkling his heavy brows. "Harwich," he added, "we appreciate your company a lot. Only we are engaged in some pretty serious business here, and it doesn't allow us to take in outsiders."

For reasons of his own, Bayley was trying to get rid of the big patrol pilot. But Harwich was inclined to be very stubborn, naturally, and faint, pleading looks from both Clara and Paul Arnold, made him doubly so, just at present.

Harwich had the aspect of a very dangerous adversary in a physical encounter; his weathered features were far from beautiful, and at certain times he had a way of grinning that made him look like a good-natured devil with a hot pitchfork hid behind his back. He turned on that grin, now.

"What's in that package sticking out of your coat-pocket, George?" he asked the fat printer breezily. "It's about the right size and shape to be the new Gyon condenser we need. I was going to buy one myself; but seeing that you've already done so, we might as well go to work installing it in the Penetrator apparatus."

"Well, all right, Harwich," Bayley growled with some slight show of timidity. "As long as you're Paul's friend, I suppose you can stick around."

"Thanks a lot, George," Harwich chuckled, as the printer set the package containing the precious Gyon condenser on a work table.

The patrol pilot was almost sure he heard faint sighs of relief from the two Arnolds, as Bayley backed down. Had they come to mistrust him too, since he had been financing them? Did they feel more at ease because he, Evan Harwich, whom Bayley could never bulldoze, was their partner now too?

The spaceman wondered, and he couldn't help wondering something else. On Clara Arnold's left hand, there was a diamond gleaming. An engagement ring. Bayley's? The way the latter had clung to the girl's arm, it couldn't very well be anybody else's. Could Clara, quiet and beautiful, ever love the boisterous, paunchy printer?

The Arnolds were a strange family, anyway. The son was ready to sacrifice his life in an effort to reach the Forbidden Moon, where his father's ashes lay entombed. The daughter? Might she not be of the same fanatical breed? Might she not be willing to marry Bayley, so that he would supply funds for their experiments?

For a moment, Evan Harwich felt a sharp, hurt ache, deep in his heart. But he fought it down. All this was none of his business. And from a heavy-glazed window slit in the ceiling of the laboratory room, a shaft of soft light from ugly Io, the Forbidden Moon, was stabbing down, appealing to his own adventurous nature.

Paul had slipped on a pair of lab coveralls. He tossed another pair to the patrol pilot. "Come on! Let's get started, Evan," he urged pleasantly. "We've got a big job in front of us, and remember you said we'd get through with it before long!"

* * * * *

True to Harwich's predictions, the rearrangement of the Energy Barrage Penetrator for far greater power than the original had possessed, did not take really a lot of time.

Within forty hours after the patrol pilot's arrival at the lab, the task of installing the Arnold apparatus in the old space ship, RQ257, was complete. The tests of the Penetrator had been made, and judged as successful as anyone could have hoped for.

The space ship stood ready there in the laboratory room, a slender, copper helix wrapped around its hull.

"All set, eh?" George Bayley boomed jovially. "Got your emergency supply-packs loaded aboard, too, eh? But you won't need them, boys," he added seriously. "You've got everything in your favor. And in five hours you'll be back here with Clara and me, at the lab with a dandy story to tell."

Bayley seemed honest and sincere, now. Evan Harwich almost felt sheepish about the matter. Maybe he'd misjudged the big, bearish printer. Anyway, he watched his every move, during the assembly and installation of the Penetrator.

Paul Arnold was whistling a little tune of confidence and exultation. Harwich's pulses beat happily, his thoughts on the enigma of the Forbidden Moon, that now must yield to the new Energy Barrage Penetrator. Superscience there on Io! Unutterable wonders! Who could guess beforehand what the Forbidden Moon's vast screen of force was meant to bar from intrusion? But maybe they would soon know!