"National Treasure: Book of Secrets" is a bit like fool's gold.

The sequel glitters, with its expanded cast now including Ed Harris and Oscar winner Helen Mirren, but scratch a little deeper and it's simply more historical hokum as a missing page from an assassin's diary sets the story into motion. Even as escapist family fun, it's pretty feeble.

This time, it's really personal as an ancestor of treasure hunter Ben Gates (Nicolas Cage) and his father, Patrick Gates (Jon Voight), is accused of being a co-conspirator in the assassination of President Lincoln.

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'National Treasure: Book of Secrets'

• Starring: Nicolas Cage, Justin Bartha, Diane Kruger.
• Rating: PG for some violence and action
• Web site: 'National Treasure: Book of Secrets'

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That is absolutely at odds with family history about Thomas Gates, and Ben doesn't want the Gates name to be mud. Or Mudd, as with the doctor who set the broken leg of John Wilkes Booth after he shot the president.

The truth squad starts with Ben and his techie pal Riley (Justin Bartha) and soon includes Ben's former girlfriend, Abigail Chase (Diane Kruger), Ben's dad and Ben's mother, a Maryland linguistics professor named Emily Appleton (Mirren) who is peeved much of the time, not that you can blame her. Or Mirren.

Emily hasn't spoken to Patrick in 32 years and the minute they see each other they start replaying some long-ago argument. How common and predictable.

This gang of five, in part or full, embarks on a globe-trotting adventure trying to stay one step ahead of the man who besmirched the Gates name. That would be Mitch Wilkinson (Harris), a black-market antiquities dealer with family roots in the Confederacy and his own interest in history.

"Book of Secrets" takes them from Washington, D.C., to Paris to London to Mount Rushmore with ridiculous ease in slipping into off-limit, supposedly secure locations and often handling precious artifacts with their bare hands. (Sure, I have my purse searched and a wand passed over my body before entering a movie preview but these folks can snoop around the Oval Office.)

"Book of Secrets" was written by the husband and wife team of Marianne and Cormac Wibberley, who shared credit on the first movie with Jim Kouf. The Wibberleys have cranked out a series of forgettable or horrible scripts (including "The 6th Day," "I Spy," "Charlie's Angels: Full Throttle" and "The Shaggy Dog") and they have a tin ear for dialogue.

Here, they and director Jon Turteltaub use actual, fascinating historical tidbits to pull us along, but what should be silly and fun turns sodden, leaden and long. The only actor who strikes the right note is Bartha as the wisecracker who knows his role is subservient to Cage, just as his character is.

On the plus side, the movie has a cartoon attached and it's perfect for holiday shoppers. It stars Goofy and is called "How to Hook Up Your Home Theater." Without naming names, although you'll recognize the big-box chain, it manages to spoof the experience in a knowing and nutty way.