DISCLAIMER: Although being a spinoff game of Zombie Fighting, this game is not as upbeat as Zombie Fighting. I repeat: this game is not as upbeat as Zombie Fighting. You beat the last evolved zombie. Or so you thought. You retract back to your house, waiting for things to go back to normal. Suddenly, you notice something. People just randomly disappear without a trace and a stench of death has been coming from the tunnel system underground. Your goal is simple. Find out what caused it.
This game comes last lorewise. Basically, the first game was the first wave of zombies. Second, enemies started evolving fast. This last game, zombies are almost gone. You deal with enemies in a tunnel. A red glow from a pit of fire is nearby, while something big grows inside of it.