The success National Treasure enjoyed at the box office in 2004 is half a conundrum. The appeal of a chase film the whole family could enjoy -- and one pretending to put a higher premium on gray matter than physical stamina -- is understandable. Linking America's foundational text, The Declaration of Independence, to a secret conspiracy involving forbidden lucre also seems tantalizing enough. But its popularity wasn't warranted by anything that actually transpired on screen.

The faux mystery surrounding its sequel National Treasure: Book of Secrets is why a small slice of the first movie's worldwide haul (almost $350 million) wasn't used to pay for a script upgrade. Why not take a chance and have the plot make sense? An outlandish scenario is essential. The challenge? Injecting just enough plausibility. But this random storyline is held together by flimsy connective tissue and barely excites us in a daft, time-killing sort of way.

Little effort to spark the imagination and engender a sense of wonder about the past appears evident here. Perfunctory and lacking in suspense, the movie uses the same formula:  rush over the essential details, distract viewers with a humorous sidekick, and have the music swell whenever hero Benjamin Franklin Gates (Nicolas Cage) prattles on about his forebears and love of country.

It's especially frustrating to see how lazy noodling can masquerade as deep thinking at the Cineplex. There's sounder logic and more genuine sleuthing in a Scooby Doo cartoon. Whereas it should suggest that decoding ciphers and solving puzzles takes time and effort, National Treasure: Book of Secrets tells kids they don't have to work hard. All you need are the services of a wisecracking computer whiz and access to a grade school history textbook.

In order to clear the name of his ancestor, falsely accused of being a co-conspirator in the assassination of Abraham Lincoln, Ben, assisted by Riley Poole (Justin Bartha), pays a visit to the Luxembourg Gardens in Paris, breaks into the Queen's study at Buckingham Palace, and kidnaps the President of the United States (Bruce Greenwood). His ultimate destination is Mount Rushmore and a lost City of Gold, although just how Lincoln's enemies and this North American version of El Dorado are connected I can't say.

The bickering between Ben and his archivist girlfriend Abigail (the shimmering Diane Kruger, also reprising her role) comes across as unbelievable as the history. They're going through a rocky patch, so he has moved out of the house and moved in with his father Patrick (Jon Voight). Abigail joins the hunt in London and later jiggles in the Oval Office to give Ben the chance to unlock a clue from the President's desk.

Producer Jerry Bruckheimer has remained loyal to his husband-and-wife writing team The Wibberleys and to his director and co-producer Jon Turteltaub. Hiring Dame Helen Mirren and Ed Harris doesn't make any appreciable difference to the movie's quality and can only tarnish their reputations.

One half expects Mirren to barge in on Ben and Abigail as they tinker with Queen Elizabeth's desk at the palace. Instead, she takes the role of Ben's mother Emily, an academic capable of deciphering pre-Colombian Native American markings. Harris plays Ben's adversary and fellow history nut -- a Confederate cracker and Blackwater-like mercenary named Mitch Wilkinson. Mitch is on hand during the movie's watery (and blurry) climax and disappoints by being insufficiently villainous.

The book of the movie's title is one supposedly passed from each U.S. president to the next. The topic of the franchise's third installment has been clumsily inserted into the tome but isn't revealed to the audience. Somewhere along the line, a character refers to "The debt that all men must pay." I'd sooner pay it than sit through a third National Treasure.

(Released by Walt Disney Pictures and rated "PG" for some violence and action.)