The Space Marine scanned the long and empty hallway, which was empty as he felt. Above him, the failing lights let out a final spark, before popping into the air like fireworks into the night sky. The name tag on his chest labeled him as John Stalvern, who had joined the UAC 14 years ago today. He knew there were demons in the base, he could smell their unholy stench, feel their darkness in the air. He couldn't see them, but he had expected them for years. His warnings to the leader of the base, Cernel Joson, had been repeated many times, but they were ignored in favor of advancing science at any cost. Even if the old Cernel decided to listen to the marine now, it was too late, far too late for now.
He thought back to his childhood, when he had watched the spacecrafts leave the earth, and soar into the great celestial unknown. Every time, he had said to his father "I want to be on the ships daddy.". But always, the answer was the same "No, you will be kill by demons". Once upon a time, he believed his father. But as he aged, he begun to doubt his fathers words. Now though, in the UAC space base, he knew there were demons. Their stench plagued his nostrils, their growls kept him awake at night, fearing for his life.
The radio on his chest sparked to life, uprising the wily vet and sending him a message. "This is Joson. You must fight the demons". Upon hearing the command, John reached for his weapon, a reliable old Palsma rifle. He trained its sights on the wall, and let loose a barrage of super-heated matter, obliterating the concrete. Walking into the room, he saw that some of the demons were slain by the collapsing structure, but others were untouched. "He going to kill us!" the surviving creatures screeched. Then, their leader, an old, jaded cyberdemon declared "I will shoot at him!". The demon brought his weapon to bear upon the marine, but too late, when he fired the rocket-missiles, the marine plasmaed at him, trying to blew him up. Above the fighting and bloodshed, the celing collapsed, as if it was stirred by the violence beneath it.
Trapped underneath a metric ton of concrete and steel, neither combatant could continue their exchange. "No!" John cried. "I must fight the demons!" His face was twisted with anger and helplessness. From his hip, the damaged radio let out one final transmission. "No John. You are the demons." John looked down at his body, and saw for the first time the battered armor, his bloodstained decaying skin, and the claws. He had become the enemy. He was a zombie.