This is not how it was supposed to be. The dead should not walk, the dead should be buried, mourned and inevitably forgotten. That is how it use to be anyway, before the government and its scientists figured out how to make the dead rise. 
They thought they had found a cure for cancer, the drug, only known as x714 had actually worked, on lab animals.
Once the FDA cleared it for human testing, we learned that it did not only kill the test subject, but, it brought them back to life, and when they came back, it was with a vengeance. 
The human race has always been fascinated with that which scares them; monsters, vampires, the things that go bump in the night. But, it wasnt until our fears became reality that we learned just how twisted some people could be. 
You would think that once x714 proved to be a failure, its creators would have haulted any further testing. This couldn't be further from the truth. Instead, they mass produced it, and within 5 years, had created an army.. of the undead.

hault doors

Lab Z - The Pit