The makers of “Unknown” probably want you to think of their film in terms of “The Bourne Identity,” but you’re more likely to be reminded of Roman Polanski’s 1988 “Frantic,” about an American whose wife disappears in Paris. In this case, Dr. Martin Harris (Liam Neeson) arrives in snowy Berlin for a biotechnology conference accompanied by his loving wife Elizabeth (January Jones). But when he has to rush back to the airport for his mislaid briefcase, he’s in a cab accident that puts him in a four-day coma. When he revives and makes his way back to their hotel, he finds his wife with another man (Aidan Quinn) who claims to be Martin Harris—and she agrees.

So is the Neeson Harris crazy, or is there some sort of conspiracy against him?

Well, since we’ve seen him arriving with his wife in Paris and have his accident, the former explanation seems unlikely, unless the film’s headed for a “Dallas”-like “It Was All a Dream” conclusion, and we know how successful that was. So the question is why he’s been written out of his own life, and the rest of the picture is devoted to his search for the answer, conducted while a troop of menacing thugs pursues him with obviously murderous intent. In the process he enlists the help of the female cabdriver (Diane Kruger)—an illegal Bosnian immigrant—who was driving at the time of the crash, as well as of an old East German spy (Bruno Ganz) recommended by his compassionate nurse (whom the thugs kill). A colleague of the true Dr. Harris at his American university (Frank Langella) is also drawn into the morass.

It would be unfair to reveal too much about the twists that the plot takes in winding its way to an explanation for the two Dr. Harrises. Suffice it to say that it grows increasingly ludicrous as it proceeds, ending up shattering the suspension of disbelief necessary for such thrillers to avoid becoming comically implausible. Before long we’re suffering through a pursuit through hospital corridors, a ridiculous car chase through the streets of the city that fails to attract the slightest police attention (though they show up posthaste after the opening cab accident), and a series of fight sequences so muddily shot and executed that it’s almost impossible to tell what’s going on in them. And without spoiling things, before it all ends we’re asked to believe in a malevolent secret organization that would have made Agatha Christie blush. Unfortunately, it seems incapable of operating efficiently although we’re told it’s always invincible, and its machinations in thus instance prove so complicated as to be nearly impenetrable. I rather suspect that most viewers will also chortle with disdain at the supposed motive behind all the sleight-of-hand, which involves a brilliant German scientist (Sebastian Koch) and the Saudi prince who bankrolls him; and they might also wonder at the fact that at the close a character who’s responsible for multiple crimes goes happily into the sunset, apparently feeling no guilt whatever—and we’re meant to be happy about it.

On the positive side, “Unknown” uses the wintry Berlin locations well; Flavio Labiano’s cinematography creates a moody, grim atmosphere that suits the material. And the opening accident is very cleverly staged (the long car chase sequence and a final scene set in a parking garage, on the other hand, are far less credible or compelling). And one can glean some pleasure from a few of the performances. Neeson isn’t at his best here, looking more haggard than troubled, and Jones is frankly a disappointment, looking a good deal like Grace Kelly but not exuding the same degree of allure. Kruger is better as the feisty illegal, and Ganz is a cantankerous delight as a character who’s unapologetic—indeed proud—of his communist past. On the other hand, Quinn makes little impression as the second Harris, and except for one sinister scene with Ganz (the movie’s cynical highlight, in fact), Langella is wasted in a part that reeks of the potboiler.

“Unknown” isn’t clever or sexy enough to bear comparison to a movie like Hitchcock’s “North by Northwest” (which it emulates in its blonde heroine and its final shot of a speeding train) or exciting enough to match the “Bourne” series it obviously aspires to—twisting itself into a narrative pretzel in the process.