Uncle Charles is killed by one of his test subjects during an underground transaction to get rid of the Trioxyn-5. The kids that made it out alive from Necropolis (now in college) return and are not too much wiser for their experience. They find a canister of Trioxyn-5 and try to figure out what it is. Knowing that it probably had something to do with Uncle Charles' experiments, Julian and his new friend Jenny have the brains to be cautious where as the other kids see it as a new party drug and an opportunity to make some quick cash. As the drug becomes more and more popular and Halloween approaches, kids are partying and overdosing on "Z". This turns hundreds of innocent costumed college students into brain thirsty zombies. It all culminates at a huge rave put on by Jenny's brother Jeremy. Zombies mistaken for costumes and two Interpol agents that are more harm than help all add to the hilarity and horror that ensues.