Lights Out by Nate Southard

Burnham State Maximum Security Penitentiary holds the worst criminals humanity has to offer. Murderers, rapists, and others who have preyed upon humanity populate the prison, creating a food chain of violence and fear. 

But something new has come to Burnham, something ancient and powerful. It is deadly and merciless, a force of pure evil. And it is hungry.

Now, those who call Burnham home must band together if they hope to survive. After years of being called monsters, they will face something much worse, and they will know how it feels to be prey.