It stars Denzel Washington (Scott's "Man on Fire" star) as Doug Carlin, an ATF agent called in to investigate the bombing of a ferryboat in New Orleans on Mardi Gras. Carlin is the sort of detective who notices things like tiny bits of plastic washed up on the shore and explosive residue on the underside of a nearby bridge. While the other agencies -- local police, FBI, etc. -- squabble over whose jurisdiction this is, Carlin looks for clues.
Then a body turns up. Lots of bodies are turning up, of course; the boat was full of passengers when it exploded. But Carlin realizes this particular victim was killed beforehand and dumped in the water so as to LOOK like one of the boat victims. Which means the killer knew the explosion was coming. Which means he's probably the one responsible for it. Find out who killed this woman, find out who blew up the ferry.
Carlin hooks up with an FBI squad, led by Val Kilmer and featuring a lot of A/V geeks, who have a nifty bit of technology to show off. Using all the surveillance cameras in the city, they're able to piece together a "movie" of what everyone in town was doing exactly 102 hours ago, in real time. All they have to do is watch this particular victim, a woman named Paula Patton (Claire Kuchever), and see who she met with prior to her death.
Now, Carlin is a genius, but it doesn't take one to see that there's more going on here than just watching surveillance tapes. That's where the sci-fi comes in, and that's where I stop talking.
Once the film establishes all the rules and sets the game in motion, it proves to be a jaunty, pulpy good time. It straddles the border between fun and ludicrous rather precariously, and it usually (I do not say always) falls on the fun side. I can't say the screenplay, by Terry Rossio ("Pirates of the Caribbean") and Bill Marsilii, completely explains all the paradoxes it introduces, but there is generally much more cleverness in evidence here than you usually get from these cat-and-mouse cop-chasing-killer capers.
Denzel Washington has played a law-enforcement officer about a dozen times now, and there's a reason for that: He's good at it. He inspires confidence as a man on the right side of the law, and in "Deja Vu" he's actually permitted to smile, rave, and be interesting. Not that the film needs carrying -- it's pretty nifty on its own -- but Washington injects it with some good old-fashioned charisma, too.