The Eden Wildlife Zoo, a zoo containing endangered animals, is having its intern orientation day, where college students applying for jobs as interns are touring the zoo. Meanwhile, some the zoo's monkeys contract an unknown disease and are taken to the clinic where the veterinarians use intracardiac epinephrine, a forbidden serum, in order to save the life of a monkey that suffered a cardiac arrest. The contagious pathogen spreads to all of the monkeys in the room, turning them into zombies with a predatory behavior towards humans. They attack the veterinarians and kill two of them, while the remaining one manages to activate an alarm.