|PLOTThe town of Dillford, Ohio, is home to three species who despise each other: humans, vampires, and zombies.
School nerd Dag sets out to lose his virginity with Lorelei, the hottest girl in school. He has issues with Rick Wilson, the baseball coach and manager of the local meat factory. Rick fired all of the human employees, including Dag's mother, and replaced them with zombies as cheap labor.
Social outcast Petra is transformed into a vampire after being bitten by Milan, the high school's playboy vampire, while they are making out. Dag's former best friend Ned is also a social outcast at high school. Following Petra's transformation into a vampire and an argument with his family, Ned visits the zombie ghetto. He allows a female teenage zombie to bite his leg, transforming him into a zombie.
Aliens invade Dillford, causing residents to believe that the vampires, zombies and humans are attacking each other. Dag and Lorelei hide in a house which is raided by a group of vampires and Lorelei is turned into a vampire by Petra. In subsequent brawls between the factions, Dag, Ned, and Petra join together and hide in Stuart Miller's basement, but Petra and Ned are overcome by hunger and eat Stuart and his mother. The aliens are able to determine their location, causing them to seek cover at the high school. Petra and Dag become trapped and make out, but he flinches and Petra accuses him of being afraid of her. The aliens find them again, and Dag realizes that the aliens can only see inorganic materials, such as their synthetic clothing. The three then strip and run to Dag's house, where they change into organic cotton clothes kept by Dag's hippie mother.
Later, Dag, Petra, and Ned are captured by the aliens. They are placed with other captured residents in a warehouse, with force fields segregating the humans, vampires and zombies. Dag, Ned, and Petra convince everyone to band together to fight the aliens.
At Rick Wilson's meat factory, the chemical "Tetrafluoraxipan" is used to transform horse cartilage into a meat-like substance. The aliens submerge in the chemical and combine to grow into a single large alien. It begins to make a speech, but the town's irritated residents interrupt, enraging it. The alien fights the town's residents who determine that the alien's weakness is ammonia.
Meanwhile, Milan corners Petra and attempts to kill her. He is stopped by Dag, who turns to werewolf. After a short brawl, Milan is accidentally killed when he lands on a wooden slab, which impales him.
As the outclassed alien is shrinking back to its mini size, it attempts to escape by spaceship while dropping a bomb to destroy the town. Ned and Dag are able to hit the bomb with a plank, returning it to the spaceship which explodes, destroying the alien menace.
Everything returns to normal for the town, and it is discovered that Lorelei is alive. However, Dag chooses to be with Petra instead. Ned appears to be happier and better adjusted as a zombie, and seems to have bonded with his star athlete brother who has also become a zombie.