With a list of oddly named characters — Rhamus Twobellies, Loaf Head, Gertha Teeth, Mr. Tiny, Mr. Tall, Monkey Girl and Evra the Snake Boy — the deliciously titled Cirque du Freak: The Vampire’s Assistant holds more than its share of promise.

An added plus: right from the start we find the title character, Darren Shan (Chris Massoglia), in his coffin, biding his time with a hand-held video game and explaining how he got into this unfortunate position.

Yet despite some inventive touches, the occasional clever line and a gazillion bucks’ worth of special effects, Cirque du Freak comes up lame, disappointingly low in both horror and comedy. Based on a series of books by the real Darren Shan, the film fizzles more often than it catches fire, spiraling down into the inevitable battle to the finish between the good vampires and the bad vampires.

Good vampires? With a shock of wild hair and a manner that’s a cross between cajoling and slightly sinister, the 200-year-old Larten Crepsley (John C. Reilly) is a good vampire. Long ago he and two friends, the now-dead Vincent and Gavner (Willem Dafoe with a pencil-mark moustache and a cadaverous face) decided to become gentlemanly vampires. Rather than killing their victims and turning them into vampires, they’d just have a little bite and take a tiny amount of blood to satisfy their hunger. Maybe that’s how Crepsley can keep his love affair sizzling with the freak show’s bearded lady (Salma Hayek).

Their cult quickly caught on among vampires, though not all of them. The killing bloodsuckers became known as the vampirese and it is these two opposing sides that a man named Mr. Tiny (Michael Cerveris), who is not tiny at all of course, hopes to exploit into an apocalyptic battle that will leave Mr. Tiny ruler of the world.

At the moment, Crepsley and his very large bright blue-and-red spider, Madame Octa, have found a family in a traveling freak show with its snake boy, monkey girl, a woman who can immediately grow back her torn-off limbs and several tiny shrivel-faced creatures in burlap robes who love to eat rats. At one inventive moment Crepsley and Madame Octa do a zany tap dance across the stage.

Into this stew of oddities arrives Darren and his mischievous best friend, Steve (Josh Hutcherson), who come to see the freak show, but wind up playing a bigger part in it than they ever could imagine. Steve instantly senses the real nature of the closeted Crepsley. And Darren, who has stolen Madame Octa, will soon pay dearly … and his family as well.

Although the setup is intriguing, the script by director Paul Weitz (About a Boy, American Pie) and New Bedford-raised Brian Helgeland (Mystic River, The Taking of Pelham 1 2 3, L.A. Confidential) doesn’t maintain the energy to make it truly gripping and truly memorable despite such nifty special effects as Crepsley’s “flit,” when he can flash across a room in an instant, or when Madame Octa gets loose in Darren’s high school, leaving lots of screeching in its wake.

Unfortunately there’s not a lot of chemistry between Reilly’s Crepsley and Massoglia’s wide-eyed and colorless Darren. The connection is necessary because Crepsley is supposed to take Darren under his wing and show him the tricks of the vampire trade. But Darren is always reluctant and holds back. The thought of drinking human blood repulses him.

The character of Steve, who is tempted by the darker side of vampire-dom, is a contrivance to build the good-bad conflict into the story, although Steve becomes a more interesting character than the vampire’s assistant. Meanwhile Mr. Tiny, always plotting on the sidelines for a vampire war, seems a not-very-well-fleshed-out figure despite his enormous fleshiness. In the 1940s Mr. Tiny would have been played by Sydney Greenstreet, who would have made him more quietly menacing.

With a batch of vampires at the center of this fantasy tale, Cirque du Freak: The Vampire’s Assistant should have had more bite. But despite all the flash, it’s surprisingly toothless.

**Cirque du Freak: The Vampire’s Assistant

Starring: John C. Reilly, Chris Massoglia, Josh Hutcherson, Jessica Carlson, Salma Hayek, Willem Dafoe.

Rated: PG-13, contains violence, adult themes.

mjanuson@projo.com