Somewhere at Hogwarts School a wizard is working on a powerful anti-mimicry spell. “Percy Jackson & the Olympians: The Lightning Thief” echoes J.K. Rowling’s mythological world so closely, with its magical young half-bloods and crowded canvas of supporting deities, that a hex must be brewing.

Percy, a teenage New Yorker, discovers that his long-absent father, a “dazzling” guy who vanished after impregnating his mom, was none other than Poseidon, god of the sea. (There are a lot of guys on the Jersey shore imitating Greek gods; this one meant it.) His heritage explains Percy’s ability to submerge in his high school pool for seven minutes, his dyslexia (which scrambles written English, but translates Greek in a flash) and his ADHD. He’s not hyper, he’s got finely honed battle reflexes.

The same could be said for Chris Columbus, director of the first two “Harry Potter” films, who paces this film like a demolition derby. There’s a ratio of one explosion, monster attack or life-and-death battle every 2.8 minutes, and Columbus makes sure they detonate on time. It leaps so breathlessly from one cliffhanger to the next that the action lacks an emotional foundation. The fireballs are great but the story feels confused in its tone and direction.

The characters are swiftly sketched in. Percy (played by the likable and reasonably believable Logan Lerman) is a decent sort who’s understandably overprotective of his mother (Catherine Keener, all wounded eyes and tender smiles) and ticked at his macho slob stepfather (Joe Pantoliano). His best friend Grover (Brandon T. Jackson) is all urban sass and urgent libido; given that he’s a satyr – goat from the waist down – it makes sense. At a summer camp/renaissance festival where apprentice heroes train, they meet Annabeth (Alexandra Daddario), an up-and-coming Xena, and the trio set off on a transcontinental road trip to find a thunderbolt stolen from Zeus.

The film is a meat-and-potatoes adventure enlivened by a few brief star turns. Pierce Brosnan is amiable as Percy’s doting schoolteacher, and Sean Bean’s petulant Zeus fits the Greeks’ preference for gods who are as selfish and shortsighted as humans.

The real fun arrives with Uma Thurman as Medusa. It’s a strong actress who can out-emote a coiffure of writhing, hissing snakes, but Thurman does it. With eyes like those, who needs lightning bolts? Steve Coogan and Rosario Dawson are in great form as the arrogant Hades and his bickering wife Persephone; hell as a bad marriage has never looked so vivid. And the inferno’s physical location on the U.S. map is a good, broad joke.

Unfortunately, there’s not enough going on in the film to sustain the needed excitement. In the race to copy “Harry Potter,” many a series pilot has been launched and crashed. Does anyone remember “Eragon” and “Inkheart”? “Percy Jackson” is better than those, but not by enough. It’s technically polished, spirited, well intentioned but curiously lacking in magic.