A rock concert awakens the legendary monster, who goes on a rampage. The event's organizer plans to kill the beast and create a tourist attraction around its stuffed body, but an environmentalist realizes the creature is the last of its species, and is determined to make sure it does not become extinct.
A fanatical animal rights activist releases giant pythons into the Everglades, believing the wild animals should be set free. When they start decimating the native animal population, an over-zealous park ranger feeds experimental steroids to wild alligators so they can fight back. The giant pythons and gargantuan alligators go on a killing spree, and it is now left up to the two feuding women to put aside their differences to put a stop to the creatures and the destruction.
Police lieutenant detective Thomas 'Thom' Randall's steady girl-friend, Dr. Jennifer 'Jen' Allen, is Dr. Aaron Michaels's main assistant on his pharmaceutical firm Bellion's research program to cure the highly contagious, fatal infection Guinin. A convicted murderer, whom Thom arrested, is one of their special drug test subjects, but escapes. The convict and Jen are affected by radioactively altered DNA from an experimental reactor used on mosquitoes which transfer quinine. The convict soon mutates into a mosquito-like monster, which sucks its victims dry. By the time Thom and his junior murder brigade partner Charlie Morrison figure out what happens, Jen starts mutating herself.
When zombies overrun San Francisco, a desperate group survives by locking themselves inside Alcatraz Prison. When the undead breach the island, our heroes are forced to return to the mainland overrun with the undead.
