You are Ivan Freeman working another boring day at the gun factory some location at the middle of nowhere in Texas. Night closes in on you strong and lacking life, for you find you and your co-workers trapped in the factory while Hell claims Earth. Aliens from a strange world known as "Xen" come to warn you, but are far too late. Demons find and their way in like spiders.
There will be a uniform color variation with the zombie cyborg and headcrabbed zombie cyborg. Doctor Death created the zombie cyborgs as a form of guard and programmed others to scavenge and rid of animals, and any resistance against Hell's will. Then the Doc made the Headcrab on accident, but found that the parasite made his robotic troops more lethal and turned humans into mindless hungry mutant zombies.