Soldier, listen! There's no time to repeat myself. The T12 virus has breached the security protocol at the Horizon Research Station. All personnel have been turned into zombies. The virus is currently contained, but it could break out and cause a catastrophe at any moment. You'll enter that dark place and destroy the station. Don't try to save bullets—kill every last zombie. The station's corridors are crawling with these creatures. It's lucky you have a recoilless machine gun. Go home. It's over.