When most of the population of Earth is infected with a virus and transformed into flesh eaters and blood drinking creatures, a group of hunters led by Tao chases the vampire zombies to eliminate them. Six non-infected survivors try to find the exit of an abandoned hospital crowded with the infected creatures, and Tao and his group help them. Meanwhile, the military command is ready to bomb the area and wipe it from the map.
Picking up immediately where Anaconda 3 left off, herpetologist Amanda Hayes finally learns her employer Murdoch's true colors when he hires a doctor to harvest a fresh supply of blood orchids to experiment with the regenerative nectar on a baby snake in order to seek treatment for his own terminal illness. Amanda is forced to secretly bring together another team of scientists whom face off against a heavily armed squad of Murdoch's men to steal the coveted orchids before the killer Anaconda hunts both parties down.