Michael Emerson and his younger brother Sam move with their recently divorced mother Lucy to the fictional small beach town of Santa Carla, California, to live with her eccentric father, Michael and Sam's grandfather.

Lucy gets a job at a video store owned by bachelor Max Lawrence. Michael becomes fascinated by Star, a beautiful girl he spots on the boardwalk, though she seems to be with the mysterious David Powers, the leader of a youth biker gang.

In the local comic book store, Sam meets brothers Edgar and Alan Frog, a pair of self-proclaimed vampire hunters. They give Sam horror comics to teach him about the undead threat they claim has infiltrated the town.

Through Star, Michael is drawn into the orbit of David's motorcycle gang. They challenge him with several tests of courage and soon offer him initiation into the gang. During a meal in their hangout, an abandoned luxury hotel sunken beneath the cliff by the 1906 earthquake, Star warns Michael not to drink from an offered bottle, warning it is blood, but he ignores her advice. Soon thereafter, Michael begins to undergo a change; his eyes are sensitive to sunlight, the smell of food revolts him, and his reflection becomes partly transparent. He develops a craving for blood and attempts to attack his brother Sam, but is stopped by Sam's dog Nanook.

Sam is initially terrified, but Michael convinces him that he is not yet a vampire and desperately needs his help. Sam deduces that, as Michael has not yet killed, he is a "half-vampire" and his condition is reversible upon the head vampire's death. Sam and the Frog Brothers initially suspect Max of being the head vampire but after he passes their "tests" they focus on David.

David tries to provoke Michael into killing but Michael repeatedly refuses. Star reveals that she and Laddie, the youngest of the gang, are also still partly human and that David had intended for Michael to be Star's first kill, sealing her fate as a vampire.

Michael leads Sam and the Frog Brothers to the gang's lair. They impale one vampire, Marko Thompson, with a stake, awakening David and the others, but the boys escape, rescuing Star and Laddie. Realizing the gang will come after them that night, the teens arm themselves with holy-water-filled water guns, a longbow and wood stakes, barricading themselves in the house. When night falls, David's gang attacks. The Frog Brothers, Sam, and Nanook take out two of the gang while Michael and David battle each other. David is impaled, but there is no change in Michael, Star, or Laddie, forcing the group to conclude they still have not accounted for the master vampire.

Lucy and Max then return home from their date and Max is revealed to be the head vampire. Max explains that he had instructed David to turn Sam and Michael into vampires so that Lucy could not refuse to be transformed herself, as his objective had been to make Lucy mother for his lost boys.

As Max pulls Lucy to him, preparing to transform her, Grandpa crashes his truck through the wall of the house, impaling Max on a wooden fence post and causing him to explode. Michael, Star and Laddie then return to normal. Amongst the carnage and debris, Grandpa casually retrieves a drink from the refrigerator and declares: "One thing about living in Santa Carla I never could stomach: all the damn vampires."