It has not been a long time since the nuclear explosion and all living things in the areas close to the reactor have been greatly affected by the radioactivity.
Every week, "cleaners" are sent to the area to prevent the monsters from being heard. You are this weeks cleaner. You have to "clear" zombies, dogs, rats and more.
You will start at the regional hospital, then go down to the streets of nuclear plant and finally reach the tunnels under the reactor.