What are Helen Mirren and Jon Voight doing soaked in a raging underground river? And why's multiple Oscar nominee Ed Harris snarling like a silent-screen baddie? How about debonair Bruce Greenwood, skulking through a cave? And what's with Harvey Keitel, as a G-man cartoonishly exclaiming, "the President's been what?!"

They're all here in the service of Nicolas Cage, himself an Academy Award-winning thespian who, in the guise of gallivanting historian Ben Gates, tears around Washington and Paris, Buckingham Palace and Mount Rushmore, in search of a lost city of gold. Yes, it's National Treasure: Book of Secrets, sequel to 2004's surprise blockbuster ($350 million in global receipts), and it's a thumping, gabby slog.

Signaling the tedium to come, the movie starts in a lecture hall, with a riveting Power Point display and the discovery of missing pages from the diary of Lincoln assassin John Wilkes Booth. Sadly for Gates and his dad (Voigt), the pages seem to implicate a Gates ancestor as one of Booth's coconspirators. But father and son believe the diary points to something else altogether: codes and puzzles that lead to a legendary American Indian treasure. And so they're off to clear the family name, and unearth a trove.

There's much more to the plot: a secret book shared by U.S. presidents; a covert alliance between Queen Victoria and a Confederate general during the Civil War; twin 19th-century desks with missing planks; the Statue(s) of Liberty (the one in Paris is key), and on and on.

Directed, as its predecessor was, by Jon Turteltaub, National Treasure: Book of Secrets is like a grade-school version of an Indiana Jones adventure. The fact that Disney has attached a Goofy cartoon short to the thing pretty much speaks to the demographic group the studio is expecting to attract, and so the level of discourse is set accordingly low.

Also along for the ride (and the paycheck) is icy Euro beauty Diane Kruger, who returns as the fashionably attired D.C. archivist Abigail Chase. For the very few folks who saw the actress last year opposite Ed Harris in Copying Beethoven, there's a small moment of amusement to be had as the two share scenes together here, illustrating the peculiar vagaries of a Hollywood career.

National Treasure: Book of Secrets *1/2 (out of four stars)

Directed by Jon Turteltaub. With Nicolas Cage, Bruce Greenwood, Ed Harris, Harvey Keitel, Diane Kruger, Helen Mirren and Jon Voight. Distributed by Walt Disney Pictures.

Running time: 2 hours, 4 mins.

Parent's guide: PG (adult themes)

Playing at: area theaters