Liam Neeson starts as Dr. Martin Harris in Unknown Dark Castle Holdings / Warner Bros. Pictures

You're Dr. Martin Harris, a botany professor at an American university, and you've come with your wife Liz to Berlin for a biotechnology conference. As she checks into the hotel, you realize you left your briefcase at the airport and hail a taxi, telling the blonde driver to step on it. An accident sends the cab careering off a bridge and into a river, from which the driver pulls you out before vanishing. A few days later you awake from a coma and bolt from the hospital to join Liz at the conference. Funny — she doesn't seem to recognize you. And the man standing next to her, she says, is Dr. Martin Harris.

Liam Neeson plays the botanist, January Jones the wife, Diane Kruger the cabbie and Aidan Quinn the other Martin in Unknown, a standard-issue conspiracy thriller that hopes to be mistaken for a Jason Bourne film — or, better yet, a sequel of sorts to Neeson's 2009 hit Taken. The new film shifts the venue from France to Germany, and it takes a while to explain why a brainy professor would have the same killer skills (bare-knuckle fighting, stunt-car driving) as Neeson's CIA operative in Taken.

Other differences: Unknown, directed with a kind of jittery glumness by Spain's Jaume Collet-Serra (Orphan), has a slightly higher IQ and a way-knottier plot. Though the result is half-cocked Hitchcock and sub-Bourne, Unknown tantalizes by the breadth of the earlier, better pictures it imitates, which speaks both to its ambitions and its limitations.

The plot, which Oliver Butcher and Stephen Cornwell adapted from a novel by Didier Van Cauwelaert, has familiar action-film mainsprings: the hero must rush to unlock some awful secret even as he tries to elude the killers who want to protect it. That involves desperate car chases through crowded streets, where Neeson and Kruger risk a thousand innocent Berliners' lives to save their own. Since Joel Silver (the Lethal Weapon series) is one of the producers, Unknown follows Silver's Law of the Impossibly Nimble Pedestrian: cars maneuver madly down sidewalks and everyone gets safely out of the way. Also obeyed is the Corollary of the Ruthless But Stupid Villain: bad guys chase and often catch up with Neeson's car, firing loads of ammo, but never think to shoot out one of its tires. Then there's the Rule of One Too Many Coincidences. It already beggars belief that the glorious Rhinemaiden Kruger would be cast as an illegal immigrant (she's supposed to be Bosnian); but how come she drove Neeson and herself off the bridge? Is that part of some grand nefarious scheme, or an out-of-the-blue case of bad luck?
Ignore the plot's dabbling in corporate espionage and find, in the movie's gnarled heart, the old existential film-noir poser: Who am I? Having left his passport in his briefcase (and his briefcase at the airport), Martin cannot prove his identity to Berlin's skeptical cops and security guards. And with only selective memories of his life before the crash, he's not totally sure who he is either. When he tries to convince the conference's keynote speaker that he's Martin, by telling him intimate parts of his life, the other Martin rattles off the same anecdotes simultaneously. Our conflicted hero is deep into the identity crisis that afflicted so many late-'40s noir heroes and which, to soldiers back from the battlefield, served as Hollywood's metaphor for the post-traumatic stress syndrome (shell shock, they called it then) that cast haunted shadows over sunny postwar America. For GIs who came home traumatized, film noir was both a validation of their anxieties and B-movie therapy to cure it.

We're not giving too much away — though, to be prudent, we'll slap a SPOLIER ALERT on this paragraph — by noting Unknown's affinities to Hitchcock's 1959 North by Northwest, in which an ordinary advertising executive, played by Cary Grant, is mistaken by international spies for a shadowy government agent named George Kaplan; to save his life he must assume Kaplan's identity and woo the spy leader's girl friend (Eva Marie Saint, whose slim, blond, beckoning air of mystery and hidden agenda Jones duplicates here). Unknown is also indebted, as so many modern thrillers and fantasies are, to the speculative fiction of Philip K. Dick — all those cyborgs who think they're human — and to the 1950 British film So Long at the Fair, where a young man disappears during the 1889 Paris Exposition and his sister (Jean Simmons) can't convince anyone he ever existed.

If the movie's who-am-I? angle has a little emotional resonance, that's thanks to Neeson. A latecomer to stardom, the Irish actor was 40 when he wowed Broadway as the hunky Swede in a revival of Anna Christie (Neeson's costar was his future wife, the late Natasha Richardson) and Steven Spielberg cast him as the star of Schindler's List. Neeson came fully matured to the movie public, and now, at 58, projects a sense of decency and a nagging conscience, an awareness that the world is a dangerous place and a weary reluctance to use action-hero fisticuffs. Unlike Harrison Ford, who usually plays a grouch with muscles, Neeson suggests the intellect of someone who might have stayed awake in college classes; he's as plausible as an Ivy League scientist as he is a thug for hire.

Well, everything is like a lot of things that came before, and Unknown doesn't add much savor to the stew. But it is the rare conspiracy thriller that ripens as the villains' organization and motives are gradually revealed. One important character shows up halfway through the movie, another very near the end. The first is Ernst Jürgen, who uses his old contacts from the Stasi, the East German secret police, to locate some pieces of Martin's identikit. Then Rodney Cole, the head of Martin's department back in the States, appears to solve the rest of the puzzle.

The deadly confrontation between these two imposing gents marks the film's most absorbing faceoff — largely because Cole is played by veteran sinister smoothie Frank Langella, and Jürgen by long-ago Euro art-film heartthrob Bruno Ganz. Admirers of the new German cinema will be pleased to spot, among the supporting cast, Sebastian Koch from The Lives of Others, Karl Markovics from The Counterfeiters, Eva Löbau from Requiem and Rainer Bock from The White Ribbon. The last two were also in Quentin Tarantino's Inglourious Basterds.

Unknown isn't in the class of any of these films, but it does rise above Taken's generic revenge story to the level of marginally satisfying winter diversion. However lethargic it is in sections, it has the kernel of a superior thriller. In your imaginary movie studio, you might almost greenlight a remake. Same cast, different director.
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