The unknown doesn't pose as much of a problem in this engaging thriller from Jaume Collet-Serra as does implausibility. Like, how probable is it that fastidious Dr. Martin Harris (Liam Neeson) would leave the briefcase containing his passport at Berlin's Tegel Airport? That he'd grab a cab to retrieve without telling his wife (January Jones)? Or that the cab would crash, putting him in a coma, and that before you can say, "Jason Bourne," he'd wake up to find that another man (Aidan Quinn) has assumed his identity and his wife doesn't recognize him? Credibility doesn't improve much after that, but when Harris has only an illegal Bosnian immigrant (Diana Kruger) and an ex-Stasi officer (Bruno Ganz) to rely on, the unknown takes over — the sinister, shifting nature of identity, memory, and guilt. The wintry recesses of Berlin add resonance, and Neeson in his incarnation as an action hero at last has a role worthy of his talent.