Cirque du Freak: The Vampire's Assistant

There’s a lot of talent behind this first-strike adaptation of the popular young-adult book series by Darren Shan, but not, unfortunately, where it counts. Screenwriter Brian Helgeland gave us “L.A. Confidential’’ and director Paul Weitz gave us “American Pie’’ and “About a Boy.’’ The supporting cast runs wide and deep, from Jane Krakowski (“30 Rock’’) as a limb-regenerating sideshow vixen to Willem Dafoe as a vampire dandy.

None of which matters when your lead actor is a dud. As Darren, the high school hero who becomes apprentice to a vampire and gets drawn into a centuries-old feud, Chris Massoglia is almost wholly charisma-free, a handsome, hesitant two-by-four who makes you appreciate the rich thespian skills of Daniel Radcliffe. Casting an unknown is always a gamble. This time the house wins.

The aggravating part is that Josh Hutcherson, a young actor of actual talent, is stuck in the second-banana role of Steve, Darren’s bad-boy best friend. The two sneak out to a mysterious freak show in which the star attraction is a vampire named Larten Crepsley, played by character actor John C. Reilly in a rare and welcome lead role. After a few plot complications, Darren is chosen as Crepsley’s right-hand man and becomes a “half-vampire,’’ which the movie more or less views as dropping out of school for a real job.

There’s some nonsense about a war between two tribes of bloodsuckers - Crepsley belongs to the good guys, who sedate and sip rather than butcher their prey - but the pleasures of “Cirque du Freak’’ are in the snappy dialogue and enthusiastic secondary performances. Dafoe has only two scenes but he makes them count as a prissy little vampire - the Franklin Pangborn of the undead. Patrick Fugit (“Almost Famous’’) plays a slithery slacker snake-boy, Salma Hayek gets to grow a computer-generated beard, and newcomer Jessica Carlson makes a very fetching monkey-girl love interest.

Reilly gives it his all, and he’s both very enjoyable and about as scary as a stubbed toe. It’s not the actor’s fault he’s a big old teddy bear, and, anyway, that fits the PG-13 marketing plan of “Cirque du Freak,’’ a movie that breaks the hero’s neck and puts him temporarily six feet under while remaining as safe as a trip to the mall. Will there be a sequel, a “Cirque du Freak: Legend of the Viable Franchise’’? Only if the filmmakers can find a lead actor who’s certifiably among the living.

Ty Burr can be reached at tburr@globe.com.