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TNT:Evilution
Though all the top management of the UAC were dead, and so were most of their personnel down to the janitors, the corporation survived, now under strict government supervision. The UAC still sought the secret to matter apportation, and continued its experiments under vastly increased safety measures.
The UAC's base was set up on one of the moons of Jupiter, hoping that the increased distance would enhance Earth's safety if something went wrong. Marines were stationed at the base, ready for anything.
The Invasion
Soon after the UAC opened its first Gate, the minions of Hell made their first attack. Suddenly, through the Gate flowed spiked, fanged, dripping techno-terrors. Meat machines flailed their armored limbs and slavered with bloodlust, seeking soft bleeding manflesh to rend. But in their seeking, they found only death. The United States Space Marine Corps was prepared for such an event, and they poured molten death into the hordes of Hell. More demons massed, hoping to overwhelm the defenders by their endless numbers. But mass alone was no match for the marines. Set up in defensive positions around the gate, the marines were able to slaughter the monsters by the hundreds, taking few losses.
As suddenly as it had begun, the invasion ended. The last flaming skull screamed through, was hit by twenty simultaneous shotgun blasts, and the chamber was silent once more, except for the dripping of blood. Hell had failed.
The research went on, more boldly, and less cautiously. All the marines received the Silver Star from a grateful government, and the UAC made an enormous contribution to the Veteran's Fund. The defensive positions were strengthened, and the marines watched closely for another attempt, all their attention drawn inward towards the Gates. They were looking in the wrong direction.
The Rain of Monsters
Hell knew more than one trick. Months after the Gate incident, the yearly supply ship came ahead of time. On radar, the ship looked far larger than usual. And it was coming from the wrong direction. Strange, but not inexplicable. The lax radar operators reported the ship's approach, and personnel went out to the landing field to meet it. But it never landed. Instead, it hovered over the base, miles in the air. The men and women looked up at it, and saw that something was terribly wrong.
The ship could not have come from Earth. It was huge, kilometers long, and was built of bone, steel, flesh, corruption, and death. It was a bio-mechano-magical construct from the depths of Hell and It had come through space for its vengeance. Enormous doors, large as football fields, irised open and hideous demons poured out, plunging to the ground and blanketing the entire base with their throbbing, pulsing bodies. They were everywhere at once. The marines' defenses, set up to prevent an attack from the direction of the Gate, were worthless. The monsters poured through the sewers, the air vents, the hallways, everywhere, rampaging, corrupting, and feasting.
Once more, the surviving humans were left as zombified brain-dead monstrosities. existing only to kill and kill and kill.
It's Up To You
Only one man escaped death or zombification. The marine commander. You. You weren't at the base when the skies opened and devastation poured from the stars. You were miles away, enjoying a walk across the moon's rough-hewn landscape. Then you heard a snortling gurgle behind you, whirled, to face one of Them. The beings that still haunted your nightmares. Your reflexes weren't dulled by your experences, and you pulled out your pistol and blew the imp to gory shreds.
Hot-footing it back to the base, you saw it all and realized what had happened in a flash. The demon ship still floated above the infested base. Your boys -- the men you'd trained to fight and kill and die as no fighting man had ever been trained before -- were dead. You were not there when it happened, to die with them.
Unlike the ancient Samurai, who chose to die with their men, you cocked your pistol. You were going to kill for your men. And if you died trying, well, you were going to die anyway, some day. Death at the fangs of demons might be the very worst way to die, but if they did manage to get you, Hell would know it had been in a fight.
The Plutonia Experiment
After Hell's catastrophic invasion of Earth, the United States took steps to prevent such an invasion from recurring. The old UAC corporation was refounded, under completely new management (since the old trustees and stockholders were all dead, this wasn't much of a problem), and sent to research tools and technologies to prevent such an incursion from happening ever again.
Though the invasion had been stopped, and the remaining demons were gradually being exterminated by mopping-up squads, it was clear that the powers of Hell remained strong. While the Spider Mastermind and Baphomet seemed to no longer threaten, who knew what else lay Outside? Waiting. Watching. Preparing.
The new UAC began working on quantum Accelerator devices, intended to close interdimensional gates at a distance and so prevent future incursions forever. The project began innocently enough. Naturally the scientists, in order to learn how to close Gates, had to relearn Gate technology first. This ability was rapidly regained. Perhaps too rapidly.
The Terror
Soon, beings from Outside had their dire attention drawn to the new experiments, and then, one day, a Gate opened in the heart of the research complex. Unnatural horrors from the pit poured in, ravening for destruction. But the UAC scientists had learned their trade. The Quantum Accelerator Device performed perfectly in its maiden test -- the invasion Gate was closed instantly and permanently when the Accelerator flicked on. A cyberdemon, halfway through, was snipped in two when the Gate closed. Earth would now be safe from literal invasion by Hell. At least, once the technology could be set up around the globe.
The next day, a ring of seven Gates opened, throughout the base, and a monstrous legion rampaged through. The Quantum Accelerator began putting out the Gates at once, and within an hour, six were closed. But the hellish army was now too strong, too numerous. The marines fought like mad dogs, but were finally pulled down by the enemies' claws. The scientists, marines, and bureaucrats were all slain or transformed into undead mankillers.
The Task
The Quantum Accelerator and its prototypes are deep inside the ravaged complex. A demon Gatekeeper guards them and mans the last Gate of Hell. The government, frantic that the Quantum Accelerator will be destroyed or used in some alien fashion upon us, has ordered all marines to the site at once, regardless of their location.
You were on leave at the beach, only a few minutes from the complex, when you got the word. You suited up, grabbed a pistol, and raced your pickup truck to the complex. When you arrived, flashes of light, howls, and chanting could be heard from the interior. Corpses were scattered everywhere. Obviously the Gatekeeper was doing something inside -- something that would soon reach some kind of awful climax.
You know that within an hour or two, an entire division of marines will arrive to assault the base with full artillery and air support. You also know that they will be too late. Far too late. The airplanes will be plucked from the sky by floating terrors, the cannons melted by diabolic rockets and fireballs, the soldiers blasted to shreds as they charge into the armored shell of the UAC buildings. In an hour or two, the monstrosities inside will have finished their awful task, and will be prepared, once more, to take on the world.
It's up to you. You have to enter the complex and stop the Gatekeeper. Alone.
