SCP Foundation

There was a containment breach at one of the facilities where SCP-008, "the zombie virus," was held. It was caused by the Chaos Insurgency, but they also enhanced the zombie virus using SCP-914, known as "the Clockwork Machine." As a result, the virus mutated and infected some of the insurgents, but it didn't turn them into zombies immediately; furthermore, it acquired the ability to infect other anomalies.

Write how you want your story to start, or if you don't want to start your own, I'll give you one:

You are a D-Class in one of the many sites, though you don't know which one. On this apparently quiet day, you haven't died yet, luckily, but that afternoon you hear an alarm and the cells open. You look outside, though you only see the alarm lights. In the distance, you hear gunshots and some screams, but you also hear something that can't be clearly distinguished through the chaos, but they sound like grunts.