It was just any other day, another testament to the mundane dreary lives of the living. No one was prepared for their coming, how could they be? They entered the bodies of the living, transforming them into blood thirsty monsters, all in an instant.
Real world scientists have accidentally opened a tear in the fabric of reality, transporting their laboratory into the game world. Unable to repair and/or refuel their equipment in this (to their minds) primitive world they are now trapped.