After weeks of ceaseless work, during which was lavished upon her every resource of mind and material afforded by three planets, the Boise was ready for her maiden flight. As nearly ready, that is, as the thought and labor of man could make her. Rodebush and Cleveland had finished their last rigid inspection of the craft and, standing beside the center door of the main airlock, were talking with their chief.

"You say that you think that it's safe, and yet you won't take a crew," Samms argued. "In that case it isn't safe enough for you men, either. We need you too badly to permit you to take such chances."

"You've got to let us go; because we are the only ones who are thoroughly familiar with her theory," Rodebush insisted. "I said, and still say, that I think it is safe. I can't prove it, however, except mathematically; because she's altogether too full of too many new and untried mechanisms, too many extrapolations beyond all existing or possible data. Theoretically, she is sound, but you know that theory can go only so far, and that mathematically negligible factors may become operative at those velocities. We do not need a crew for a short trip. We can take care of any minor mishaps, and if our fundamental theories are wrong, all the crews between here and Jupiter wouldn't do any good. Therefore we two are going--alone."

"Well, be very careful, anyway. Start out slow and take it easy."

"Start out slow? We can't! We can't neutralize half of gravity, nor half of the inertia of matter--it's got to be everything or nothing, as soon as the neutralizers go on. We could start out on the projectors, of course, instead of on the neutralizers, but that wouldn't prove anything and would only prolong the agony."

"Well, then, be as careful as you can."

"We'll do that, Chief," Cleveland put in. "We think a lot of us, and we aren't committing suicide just yet if we can help it. And remember about everybody staying inside when we take off--it's barely possible that we'll take up a lot of room. Good-bye to all of you."

"Good-bye, fellows!"

The massive insulating doors were shut, the metal side of the mountain opened, and huge, squat caterpillar tractors came roaring and clanking into the room. Chains and cables were made fast and, mighty steel rails groaning under the load, the space-ship upon her rolling ways was dragged out of the Hill and far out upon the level floor of the surface before the tractors cast off and returned to the fortress.

"Everybody is under cover." Samms informed Rodebush. The chief was staring intently into his plate, upon which was revealed the control room of the untried super-ship. He heard Rodebush speak to Cleveland; heard the observer's brief reply; saw the navigator throw his switches--then the communicator plate went blank. Not the ordinary blankness of a cut-off, but a peculiarly disquieting fading out into darkness. And where the great space-ship had rested there was for an instant nothing. Exactly nothing--a vacuum. Vessel, falsework, rollers, trucks, the enormous steel I-beams of the tracks, even the deep-set concrete piers and foundations and a vast hemisphere of the solid ground; all had disappeared utterly and instantaneously. But almost as suddenly as it had been formed the vacuum was filled by a cyclonic rush of air. There was a detonation as of a hundred vicious thunderclaps made one, and, through the howling, shrieking blasts of wind, there rained down upon the valley, plain and metaled mountain a veritable avalanche of debris: bent, twisted, and broken rails and beams, splintered timbers, masses of concrete, and thousands of cubic yards of soil and rock. For inertia and gravitation had not been neutralized at precisely the same instant, and for a moment everything within the radius of action of the iron-driven gravity nullifiers of the Boise had continued its absolute motion with inertia unimpaired. Then, left behind immediately by the almost infinite velocity of the cruiser, all this material had again become subject to all of Nature's everyday laws and had crashed back to the ground.

"Could you hold your beam, Randolph?" Samm's voice cut sharply through the daze of stupefaction which held spellbound most of the denizens of the Hill. But all were not so held--no conceivable emergency could take the attention of the chief ultra-wave operator from his instruments.

"No, sir," Radio Center shot back. "It faded out and I couldn't recover it. I put everything I've got behind a tracer on that beam, but haven't been able to lift a single needle off the pin."

"And no wreckage of the vessel itself," Samms went on, half audibly. "Either they have succeeded far beyond their wildest hopes or else ... more probably...." He fell silent and switched off the plate. Were his two friends, those intrepid scientists, alive and triumphant, or had they gone to lengthen the list of victims of that man-killing space-ship? Reason told him that they were gone. They must be gone, or else his ultra-beams--energies of such unthinkable velocity of propagation that man's most sensitive instruments had never been able even to estimate it--would have held the ship's transmitter in spite of any velocity attainable by any matter under any conceivable conditions. The ship must have been disintegrated as soon as Rodebush released his forces. And yet, had not the physicist dimly foreseen the possibility of such an actual velocity--or had he? However, individuals could came and could go, but Triplanetary went on. Samms squared his shoulders unconsciously, and slowly, grimly, made his way back to his private office.

He had scant time to mourn. Scarcely had he seated himself at his desk when an emergency call came snapping in; a call of such import that his secretary's usually calm voice trembled as she put it on his plate.

"Commissioner Hinkle is calling, sir," she announced. "Something terrible is going on again, out toward Orion. Here he is," and there appeared upon the screen the face of the Commissioner of Public Safety, the commander of Triplanetary's every armed force--whether of land or of water, of air or of empty space.

"They've come back, Samms!" the Commissioner rapped out, without preliminary or greeting. "Four vessels gone--a freighter and a passenger liner, with her escort of two heavy cruisers. All in Sector M; Dx about 151. I have ordered all traffic out of space for the duration of the emergency, and since even our warships seem useless, every ship is making for the nearest dock at maximum. How about that new flyer of yours--got anything that will do us any good?" No one beyond the "Hill's" shielding screens knew that the Boise had already been launched.

"I don't know. We don't even know whether we have a super-ship or not," and Samms described briefly the beginning--and very probably the ending--of the trial flight, concluding: "It looks bad, but if there was any possible way of handling her, Rodebush and Cleveland did it. All our tracers are negative yet, so nothing definite has...."

He broke off as a frantic call came in from the Pittsburgh station for the Commissioner, a call which Samms both heard and saw.

"The city is being attacked!" came the urgent message. "We need all the reinforcements you can send us!" and a picture of the beleaguered city appeared in ghastly detail upon the screens of the observers; a view being recorded from the air. It required only seconds for the commissioner to order every available man and engine of war to the seat of conflict; then, having done everything they could, Hinkle and Samms stared in helpless, fascinated horror into their plates, watching the scenes of carnage and destruction depicted there.

The Nevian vessel--the sister-ship, the craft which Costigan had seen in mid-space as it hurtled earthward in response to Nerado's summons--hung poised in full visibility, high above the metropolis. Scornful of the pitiful weapons wielded by man she hung there, her sinister beauty of line sharply defined against the cloudless sky. From her shining hull there reached down a tenuous but rigid rod of crimson energy; a rod which slowly swept hither and thither as the detectors of the amphibians searched out the richest deposits of the precious iron for which the inhuman visitors had come so far. Iron, once solid, now a viscous red liquid, was sluggishly flowing in an ever-thickening stream up that intangible crimson duct and into the capacious storage tanks of the Nevian raider; and wherever that flaming beam went there went also ruin, destruction, and death. Office buildings, skyscrapers towering majestically in their architectural symmetry and beauty, collapsed into heaps of debris as their steel skeletons were abstracted. Deep into the ground the beam bored; flood, fire, and explosion following in its wake as the mazes of underground piping disappeared. And the humanity of the buildings died: instantaneously and painlessly, never knowing what struck them, as the life-bearing iron of their bodies went to swell the Nevian stream.

Pittsburgh's defenses had been feeble indeed. A few antiquated railway rifles had hurled their shells upward in futile defiance, and had been quietly absorbed. The district planes of Triplanetary, newly armed with iron-driven ultra-beams, had assembled hurriedly and had attacked the invader in formation, with but little more success. Under the impact of their beams the stranger's screens had flared white, then poised ship and flying squadron alike had been lost to view in a murkily opaque shroud of crimson flame. The cloud had soon dissolved, and from the place where the planes had been there had floated or crashed down a litter of non-ferrous wreckage. And now the cone of space-ships from the Buffalo base of Triplanetary was approaching Pittsburgh, hurling itself toward the Nevian plunderer and toward known, gruesome and hopeless defeat.

"Stop them, Hinkle!" Samms cried. "It's sheer slaughter! They haven't got a thing--they aren't even equipped yet with the iron drive!"

"I know it," the commissioner groaned, "and Admiral Barnes knows it as well as we do, but it can't be helped--wait a minute! The Washington cone is reporting. They're as close as the other, and they have the new armament. Philadelphia is close behind, and so is New York. Now perhaps we can do something!"

The Buffalo flotilla slowed and stopped, and in a matter of minutes the detachments from the other bases arrived. The cone was formed and iron-driven vessels in the van, the old-type craft far in the rear, it bore down upon the Nevian, vomiting from its hollow front a solid cylinder of annihilation. Once more the screens of the Nevian flared into brilliance, once more the red cloud of destruction was flung abroad. But these vessels were not entirely defenseless. Their iron-driven ultra-generators threw out screens of the Nevians' own formulae, screens of prodigious power to which the energies of the amphibians clung and at which they clawed and tore in baffled, wildly coruscant displays of power unthinkable. For minutes the furious conflict raged, while the inconceivable energy being dissipated by those straining screens hurled itself in terribly destructive bolts of lightning upon the city far beneath.

No battle of such incredible violence could long endure. Triplanetary's ships were already exerting their utmost power, while the Nevians, contemptuous of Solarian science, had not yet uncovered their full strength. Thus the last desperate effort of mankind was proved futile as the invaders forced their beams deeper and deeper into the overloaded, defensive screens of the war-vessels; and one by one the supposedly invincible space-ships of humanity dropped in horribly dismembered wreckage upon the ruins of what had once been Pittsburgh.