Teenager Darren Shan is an excellent student and the pride and joy of his perfect middle-class family, but his best friend is the reckless Steve. When they receive a flyer with an advertisement for a freak show, they sneak to the theater to see the attractions. The star attraction is a vampire called Larten Crepsley, who performs with a colorful yet very lethal spider. After the show, Darren tarries to see the spider and overhears Steve unsuccessfully trying to convince Larten to transform him into a vampire. Darren steals Larten's spider, which later bites Steve. In seeking an antidote from Larten, Darren accepts a deal to become his half-vampire assistant.
Teenager Darren Shan meets a mysterious man at a freak show who turns out to be a vampire. After a series of events, Darren must leave his normal life and go on the road with the Cirque du Freak and become a vampire.
- Darren Shan is a regular teenage kid. He and his brooding friend Steve hear about and attend a rare freak show coming to town - the "Cirque du Freak" - where they see many strange acts, including a wolf-man, a snake-boy and a bearded lady.
Steve and Darren think it all a joke until a vampire, Larten Crepsley (whom vampire-aficionado Steve recognizes) comes on with a very poisonous performing spider. Slipping away from a police raid after the show, the boys split up. Darren, due to his infatuation with spiders (as strong as Steve's infatuation with vampires), sneaks backstage to examine Larten's caged spider more closely. While hiding in a closet, he overhears Steve begging Mr. Crepsley to be made a vampire and become his apprentice. Mr. Crepsley tests Steve but finds he has "bad blood" and will not transform him. Steve becomes angry and threatening before being thrown out.
Escaping the theater with Larten's spider, Darren quickly accepts a ride home from a retund stranger - Mr. Tiny - who seems to have designs on Darren and vampires (and, very conveniently, just happens to have Darren's bicycle in the trunk of his limo).
Next day, Darren takes the spider to school with him. Steve finds out and accidentally drops the cage in the middle of the halls. The spider gets out, panics the students, bites Steve and escapes. Steve is rushed to the hospital where doctors say that there is nothing they can do.
Darren sees Mr. Crepsley about the possibility of an antidote. The vampire agrees to give him the only cure if Darren agrees to become his half-vampire assistant. Darren complies, and Steve gets the cure.
Steve recovers but starts to realize that Darren is now part vampire, becoming angry and jealous and feeling betrayed. Darren concurrently develops a taste for raw meat and his little sister's blood and comes to know that he can't stay home anymore.
Larten stages Darren's death and Darren is buried (with Steve - infuriated at being left out and left behind - noticing signs at the funeral that all is not as it seems). Mr. Crepsley comes to dig up Darren and deliver him to the circus freak encampment of Mr. Tall.
As Darren begins a life of chores amid his new family at the freak camp, Steve, seething, becomes ripe pickings for Mr. Tiny, who appreciates the kid's violent nature.
Following a visit from the ominous Mr. Tiny, Larten begins Darren on lessons in vampire fighting, but Darren's avoidance of drinking blood keeps him physically weak and incapable of full fighting power. Meanwhile, Steve gets initiated among the vampaneze (aggressive, violent, victim-killing vampires). His first assignment: a late-night visit to his least-favorite school teacher.
Four vampaneze visit the freak camp. Unable to take Darren, they take monkey girl Rebecca, of whom Darren has grown fond. Meanwhile, Steve and Mr. Tiny pay a visit to Darren's parents and abduct them as well.
Against his wishes, Larten heads back to the theater where Darren confronts vampaneze Murlaugh and Steve, fighting for the survival of Rebecca and Darren's family while Mr. Tiny enjoys watching the groundwork form for a war between vampires and vampaneze.