If imitation is the sincerest form of flattery then Dan Brown, author of The Da Vinci Code, should take John Turteltaub's family adventure as a huge compliment.

The film's screenwriters, Jim Kouf, Cormac Wibberley and Marianne Wibberley, have begged, borrowed and stolen from Brown's best-selling thriller to create their own modern-day treasure hunt.

Like The Da Vinci Code, National Treasure spins a yarn about secret brotherhoods, hidden cyphers and such nonsense, re-setting the action in and around some of America's most famous monuments.

Surprisingly for a Jerry Bruckheimer-produced blockbuster, the film is light on action; it's lighter still on logic, galloping gung-ho from one clue to the next.

The hero of the tale is Benjamin Franklin Gates (Nicolas Cage), who belongs to a long line of treasure hunters.

Like his grandfather John Adams (Christopher Plummer) and father Patrick (Jon Voight) before him, Ben has devoted his entire life to searching for the treasure of the legendary Knights Templar, a billion-dollar bounty beyond the wildest imagination, believed to be hidden somewhere in America.

The only clues to the treasure's whereabouts are a series of cryptic riddles and codes, each more devious than the next.

Aided by techno-wizard best-friend Riley (Justin Bartha) and National Archives conservator Abigail Chase (Diane Kruger), Ben realises that the next clue is hidden somewhere on the back of the Declaration Of Independence - the most closely guarded document in the whole of America.

Regardless of the danger, Ben sets about stealing the Declaration in order to continue his globetrotting quest and to prevent ruthless adversary Ian Howe (Sean Bean) from stealing the map and the booty for himself.

The hunt is on...

National Treasure is actually quite an entertaining romp, sacrificing plausibility for the sake of romance and thrills, but not so much that the plot descends into farce.

Characters are sketched in broad strokes and the relationships between them develop in only the simplest terms, including a lukewarm romance between Ben and Abigail.

Cage isn't the archetypal action hero - he almost seems to be wheezing during the chases - but he plies a nice line in knowing smirks.

Kruger's love interest shows a pleasing amount of intelligence and Bartha dutifully plays the comedic sidekick, who can barely contain his delight when he recalls a fact which the others do not.

Turteltaub maintains a brisk pace but at 131 minutes, the film is overlong and may leave some younger viewers feeling restless.

They may need to plunder the hidden treasures of the concessions stand.

Rating: 6/10