Percy Jackson and the Lightning Thief (PG)

FORGET dark. To hell with moody. What happened to plain old good fun?

There's very little of it about these days - just look at the Harry Potter series.

Each instalment tops the last in length and gloominess. I wouldn't be surprised if Deathly Hallows turns out to be Harry digging up maggot-ridden corpses for five hours while listening to Radiohead. But Percy could well be the man to take us away from all that - and back to the rip- roaring highs of the first Potter film.

Like Harry, Perce comes from a series of kids books - namely Percy Jackson & The Olympians by US author Rick Riordan.

Our Perce, basically a magic Zac Efron, is a young New York lad fathered by a Greek god on shore leave.

The novels have been a big hit in the US (although not by Potter or Twilight standards) and the good folks at Twentieth Century Fox are hoping the film of the first book will kick-start a fantasy franchise that picks up the baton from the Hogwarts posse.

And can it? Well, with my critic's hat on, I've got to admit it has some problems.

But my critic's hat fell off shortly after I read in the credits: "Co-starring Steve Coogan as Hades, God of the Underworld."

And I didn't bother replacing it because - for all the faults - this is a seriously entertaining piece of work.

As tends to be the case with book-to-film adaptations, there's a fair bit of clunky dialogue to get the plot set up, and here it's as bad as you've ever heard. "How's your DYSLEXIA?" asks Percy's mum (Catherine Keener) five minutes in. "I think it's getting worse because of my ADHD," says Perce (18-year-old Logan Lerman).

Doesn't seem to have affected your ability to TELEGRAPH PLOT POINTS LIKE A SEMAPHORE, pal.

Although PJ has no idea he's the son of Poseidon, the Greek god of the seas, Zeus's lightning bolt has gone missing and for reasons that are never quite clear, Percy falls under suspicion.

So, after he's dive-bombed in a museum by a magical beast hunting for the bolt, he's told about his heritage and packed off to Camp Half-Blood - a training ground for young demigods. (This might sound suspiciously familiar but the book was written in 1994, long before the first Potter tome).

Here, Percy learns how to use his powers under Chiron the centaur - our old pal Pierce Brosnan. And it's nice to see Brozza playing a man with the body of a horse.

Mainly cos it's a step up from Mamma Mia, where he was playing a man with the voice of a horse.

Meanwhile, Percy's mum gets kidnapped by Hades, who looks a lot more like Tommy Saxondale than the statues suggest.

So Percy and pals Grover (Brandon T Jackson) and Annabeth (Alexandra Daddario), go to save her.

And along the way they find out what happened to the missing lightning bolt and bump into dad-pleasing bit-parters like Rosario Dawson as Persephone - who can be the Dread Queen of MY underworld any day.

The whole thing's given a massive fun injection by some brilliantly enjoyable action scenes - including a showdown with Uma Thurman's Medusa and a great casino- based sequence - which carry the audience from one pacy encounter to the next.

It also gets a leg-up from the supreme likeability of the main cast.

Logan Lerman might not have much of an acting CV but he's got great screen presence and a very charming face too.

Plus, Brandon T Jackson's "funny sidekick" character is funny. Really. "There are lots of demigods around, and I'm not naming names but some of them are famous," he explains. "Like, White House famous." (OK - he tells it better than I do.)

It's perhaps no surprise that Lightning Thief matches the first Harry film in style and tone. Both were directed by Chris Columbus, who usually delivers on the family front (he also captained Home Alone and Mrs Doubtfire).

And while the ending may be hobbled by more of that clunky dialogue, at that stage I was enjoying the ride too much to care.

It's not often that a film can win a pass on charm and fun alone. 17 Again did it. The first Alvin and the Chipmunks did it. Mamma Mia wrote the book on doing it.

And Percy Jackson does it too.

Yes, it's got scripting issues, and no, it's not the most complex, multi-layered piece of family filmmaking out there.

But it's fantastic fun, it knows its Greek mythology, and it's a very promising start to a franchise. More of the same, please.

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