Nick Cage is Gates, a treasure hunter (oh, excuse me... treasure "protector", whatever that means) who is descended from a long line of treasure hunters. One of his ancestors had been given a clue to the whereabouts of a huge treasure that our Founding Fathers, most if not all Freemasons, had decided to hide because they just didn't want to finance their Independence all that badly.
The first clue turns out to be in a long-lost ship hidden in the Arctic. Gates and his crew, consisting of financier Ian (Sean Bean), Movie Dork Riley (Justin Bartha of the immortal "Gigli") and a couple of faceless lackeys, enter the cargo hold of the ship. They immediately spill out tons of gunpowder all over the floor, not that this is significant in any way. At last they find the clue (a skeleton is hovering over it) and it turns out to be a pipe with writing... on it. Sort of. Don't ask me to explain.
It's a riddle, and despite the fact that his expedition is clearly miffed at not finding the actual treasure, Gates wanders around yammering to himself about the meaning of the riddle, in this frozen cargo hold, while the crew just stands around slack-jawed. I mean, come on. Someone should have been a little vocal in their disappointment of coming all the way to the freaking Arctic and not finding anything interesting, but they just stand there as Gates enters his own world, solving the riddle.
The next clue turns out to be on the Declaration of Independence. Ian decides to steal it. Gates is appalled. Various characters deliver gratingly obvious exposition (get used to it). All this leads to Ian's lackey pulling a gun on Gates, and the gunpowder going off in a big explosion. (oh, that's why they spilled all the gunpowder! Huh!!) Ian and his henchmen make their escape, and Gates and Movie Dork Riley walk nine miles in subzero temperatures to an Inuit village in order to stop them.
To stop them, Gates concludes after trying the FBI and Super Archivist Abigail Chase (Diane Kruger), Gates and Riley must steal it themselves. Riley then tells Gates in excruciating detail why they can not steal the Declaration, because it's so protected with metal and laser eyes and high tech security blah blah. Gates then tells Riley that there's an opportunity to steal it from the Preservation Room. Does Riley know what the Preservation Room is, Gates asks? "A place where they make jams and jellies?" I am not kidding; that's the actual line. Bartha doesn't deliver it like a joke, either. So Riley does all this research about the Library of Congress and the Archives and water and sewage, fercryinoutloud, but doesn't know what the Preservation Room is. This pretty much indicates what level this script is on.
To make the rest of this short, Gates does in fact make off with the D of I, in a ridiculous break-in that could only happen in a movie. (I also hate the way they depict computer monitor technology in movies -- full of improbable and impractical graphics and fonts.) Abigail Chase ends up tagging along for convenience's sake, and as an obvious "love interest" angle. At one point, the three of them, on the run from the law, discuss all their plans really loudly in a clothing store, surrounded by people.
A series of clues and the kidnapping of Gates' father, played by a dyspeptic Jon Voight, leads good guys and bad guys alike to a huge Indiana Jones fun-house located underneath New York City. Odd that the subway builders never found this thing. Gates and Gates Senior lead Ian off on a wild goose chase. Ian believes they're trapped in a cul-de-sac and leaves them there. However, after they're gone, Riley asks how they're going to get out. Gates...
... oh boy ...
... presses a button and a door opens. No, I'm serious. A button, like they might have on a vacu-flush lavatory in an office building. Good thing he knew where that was. Anyway, after some more knob-twiddling, they find this immense treasure room (remember, this is all underneath Manhattan!) full of all sorts of historyish golden things. Riley gets to deliver a really stupid line. Again. And FBI officer Harvey Keitel forgives them, arrests Sean Bean, and allows the two chemistry-less leads to get married.
For any viewer, I think it would be hard to ignore all the exposition, the leaps of logic, and the stereotyped characters for very long. Though some of its exposition involves nice history lessons inserted into conversation at random moments. I'd like more conversations like that in my life.