Harry Potter meets Clash of the Titans in Percy Jackson & The Olympians: The Lightning Thief, the first installment of Rick Riordan’s fantasy pentalogy, directed by Chris Columbus. The target audience for Percy Jackson & The Olympians has never seen Clash of the Titans, of course. That they have seen Harry Potter goes without saying.

Perhaps the most refreshing thing about The Lightning Thief is that Percy is a boy hero who naturally takes the initiative. J. K. Rowling called Harry Potter “The Boy Who Lived,” but too often, as I’ve noted, a more accurate moniker would be “The Boy Things Happen To.” Where Harry often wound up being a passive protagonist in his own adventures, Percy sets off on a quest to rescue his mother from the domain of Hades. I’m not saying it’s the best plan, but at least he’s trying.

The story is overtly derivative of Rowling’s creation. Percy (Logan Lerman) has an oppressive stepfather (rather than a whole family of Dursleys) who gets unexpected comeuppance from a representative of a world unknown to Percy, a guide charged with ushering Percy to his new life. Harry’s adventures begin when he discovers his wizarding parentage; Percy’s life changes when he learns that he is a demigod, the son of Poseiden.

As Harry was taken to Hogwarts, Percy is brought to a training camp for demigods. Percy even has two sidekicks, a boy and a girl. Annabeth Chase (Alexandra Daddario), the daughter of Athena, is no Hermione, or perhaps Alexandra Daddario is no Emma Watson, I’m not sure. But I think I like Grover Underwood the satyr (Brandon T. Jackson) better than Ron Weasley, or maybe the older Ron of the latter Potter movies is grating on me.

The backdrop of Greek mythology makes an enjoyable change of pace from the medieval fantasy magic of the Potter stories. The Lightning Thief makes the most of the Hydra, Hermes’ winged footgear, and especially Medusa, played by Uma Thurman with a hammy gusto that’s as delightful here as it was atrocious in Batman and Robin. I’m not sure Thurman quite eclipses Ray Harryhausen’s stop-motion creature effects in Clash of the Titans as my favorite big-screen Medusa, but she comes close, which is saying something.

Medusa only gets one scene, though, and she’s one of the film’s jucier adult parts. The Potter movies may center on a trio of teenagers, but it’s the likes of Alan Rickman, Maggie Smith, Robbie Coltrane and others who make them as fun as they are for grown-ups. The Lightning Thief comes up short here.

Plot holes multiply like hydra heads. The villain’s scheme makes no sense. The “lightning thief” has stolen Zeus’s thunderbolt, knowing that this affront will lead to war among the jealous, petty gods. But then the thief impulsively decides to involve Percy in his plans in a way that has an extremely high chance of failure, adds nothing to his original plan, and greatly weakens his ability to achieve his ultimate goals.

While I don’t mind the portrayal of the Greek gods as petty and selfish, I’m less comfortable with the way the fantastical plot points dovetail with Percy’s messy home life. Other kids have deadbeat dads, but Percy’s father had to leave because Zeus insisted that mortal attachments were humanizing him, and he needed to take care of divine business. And Percy’s mother got remarried to a smelly, abusive jerk because — yes, really — his body odor helped mask the scent of Percy’s half-divine blood from monsters. See, kid, it’s not that Daddy was a rat and Mommy is codependent, it’s that Daddy loved you so much it might have upset the balance of the universe, and Mommy is secretly using that abusive jerk to protect you.

On the other hand, Percy’s initial super-power, the ability to sit at the bottom of the swimming pool for seemingly as long as he wants to, is kind of cool. That’s how we first meet him: calm, serene, in silence and solitude — not alienated like Dustin Hoffman at the bottom of his parents’ pool in The Graduate, but simply in his element … the way any kid, especially one with troubles like Percy’s, would want to be.

A longer version of this review is available at Decent Films.