It's the story of Joe, an ex-inmate used as a specimen for a mad experiment. His right arm was removed and replaced with a gatling gun. He managed to escape the prison while it was under attack by zombies. Then he teamed up with a mysterious doctor, and he followed the trail to an abandoned factory where found evidence that all this mayhem started in Central city. Now Joe's on his way, following an underground route that will lead him to the heart of the city.