A group of terrorists steal some nerve toxin from a secret military base and it accidentally gets into and contaminates a city's water supply. Now all the people of the city are turning into flesh craving zombies and the chaos starts to erupt.

Lucio Fulci was originally the director of Zombi 3, but after having irreconcilable differences with the producers he left the set. Bruno Mattei was asked to come in and pick up the pieces to finish the film.