Darren Shan is just a typical teenager, until he and his somewhat morose friend, Steve, decide to check out the peculiar "Cirque du Freak" freak show in their town. The duo is entranced by a series of bizarre performances featuring a wolf-man, a snake-boy, and even a bearded lady. However, their sense of humor quickly fades when a vampire named Larten Crepsley takes the stage with a venomous spider, capturing Steve's immediate attention due to his passion for the supernatural.
After the excitement turns into chaos when the police raid the show, the boys separate. Driven by his fascination with spiders—equal to Steve's obsession with vampires—Darren sneaks backstage to get a closer look at Crepsley's spider. While hiding, he overhears Steve pleading with Mr. Crepsley to transform him into a vampire and become his apprentice. Unfortunately, Mr. Crepsley discovers that Steve has “bad blood” and refuses to grant his wish, leading to a furious confrontation.
After an unexpected ride home with the enigmatic Mr. Tiny, who conveniently has Darren's bike in his car, the next day becomes a nightmare when Darren brings the spider to school. When Steve accidentally drops the cage, the spider escapes, causing a frenzy and ultimately biting Steve. Rushed to the hospital, he is declared beyond help. In desperation, Darren seeks out Mr. Crepsley, who offers him a treatment—but only if Darren agrees to become his half-vampire assistant. Agreeing to the deal, Darren watches as Steve receives the cure and recovers, but resentment soon festers in Steve's heart as he realizes that Darren now harbors vampiric traits, feeling betrayed in the process.
As Darren begins to grapple with his new identity, marked by an insatiable hunger for raw meat and even his sister's blood, he recognizes that he can no longer live at home. Mr. Crepsley stages a mock funeral for Darren, and he is buried while Steve watches, sensing something is amiss. Unearthing Darren, Crepsley introduces him to the unique community of the freak camp overseen by Mr. Tall.
While adjusting to life among his new companions, including his newfound affection for monkey girl Rebecca, Darren's challenges continue. He undergoes rigorous training with Larten, attempting to master the art of vampire combat, but his aversion to consuming blood leaves him physically diminished. Meanwhile, Steve's path diverges dramatically as he is lured into the violent world of the vampaneze led by Mr. Tiny, which culminates in a chilling assignment against an old teacher.
The tension amplifies when four vampaneze invade the freak camp, capturing Rebecca. In a desperate bid to save her, Darren faces off against Murlaugh and Steve, unraveling a fierce battle that sets the stage for a looming war between the vampires and the vampaneze, while Mr. Tiny revels in the chaos that unfolds.
