Bloom & Doom seed Co. was one of the most succesful seed companies out there. They also had a medical department. They were trying to mutat humans like the mutated plants.(Like the plants in Game) But something went wrong. Horribly wrong, Disasterly wronng.
The mutation did work. Just not in the way expected. The virus would only work after death. Then, the dead specimen woul rise as the undead and feast upon a victim's Brain. (Spreading the virus)
The Bloom & Doom Co could not find away to stop them. But one scientist, David Car (:D), had the idea to use the mutant plants against the Zombies. But sadly, after that Dave left to live in his house for his last days.
Soon, the Zombies overrun the nation, and soom learned to fly planes over seas. Starting the final days. There was an intern ( Later the player ) who had collected samples of mutant plants before fleeing the building, leaving for his house.