With its impressive pedigree, “Cirque du Freak: The Vampire’s Assistant” should have been a show dog.

Instead it’s a mutt.

What a cast: John C. Reilly, Willem Dafoe, Salma Hayek, Ken Watanabe, Ray Stevenson, Orlando Jones, Jane Krakowski.

Things are no less impressive on the other side of the camera: direction by Paul Weitz (“American Pie,” “About a Boy”) and a screenplay by Weitz and Brian Helgeland (“L.A. Confidential,” “Mystic River”) from Darren Shan’s popular series of “Cirque du Freak” books.

But the film is a botched job that never finds the right tone or establishes an engaging narrative.

Good teen Darren (played with stifling blandness by newcomer Chris Massoglia) and his best bud, bad boy Steve (Josh Hutcherson), sneak out one night to take in a traveling freak show populated with grotesque characters.

Steve recognizes ringmaster Crepsley (John C. Reilly) as a famous vampire he’s read about. After the show the perennial malcontent begs Crepsley to make him a bloodsucker. Ironically it’s squeaky clean Darren who is tapped for the dubious honor, becoming the vampire’s assistant. Feigning his own death, he leaves behind family and school and joins the freaks’ winter camp.

Meanwhile Steve, furious at not getting his own fangs, falls in with fat, sardonic manipulator Mr. Tiny (Michael Cerveris), whose goal is to reignite a war between the two clans of vampiredom: the bad guys who kill people and the good guys – like Crepsley – who only take a sip and leave their victims alive.

“Cirque” wants to be tongue-in-cheek amusing but never finds a consistent voice. It’s stranded somewhere between dorky teen comedy and f/x pigout. It’s not funny or dark – and certainly not darkly funny.