The Vampire's Assistant, based on the popular series of books by Darren Shan called The Saga of Darren Shan, is a fantasy-adventure about a teenager who unknowingly breaks a 200-year-old truce between two warring factions of vampires. Pulled into a fantastic life of misunderstood sideshow freaks and grotesque creatures of the night, one teen will vanish from the safety of a boring existence and fulfill his destiny in a place drawn from nightmares.
Darren Shan and his best friend, Steve, get tickets to a very elusive freak show. At the end of the show they meet Larten Crepsley (John C. Riley) a two-hundred-year old vampire. After the show, Steve stays and tells Darren to go on without him. Darren wants to see what Steve is up to and watches from the shadows. Steve tells Crepsly he knows who is by recognizing him from his many comic books and wishes to be a vampire. Larten tells him his blood is evil and Steve swears revenge for having his immortality refused. Days pass, and Steve said nothing. Darren is still amazed about the spider Larten performed with. Darren steals the spider and gets it to perform for him. Darren was showing Steve his new pet when his sister came in and startled the spider, making it bite Steve. Darren goes back to return the spider where he is greeted by none other than Mr. Crepsley. There, Mr. Crepsley tells Darren that the only way he will give him the antidote is if he joins him as his assistant and become a half-vampire. Darren accepts Mr. Crepsley's offer.