Writer-director David Mamet (House of Games, Things Change) has crafted a mesmerizing thriller, and he's done it the hard way: The suspense evolves from a philosophical search into the nature of identity. Joe Mantegna delivers a brilliant, multifaceted performance as Bobby Gold, a career cop who represses his Jewishness until a black officer calls him a kike. Gold is furious, not at the word but at the tone. His fury mounts when he's yanked off the hunt for a cop killer and told to investigate…