Native Speaker is largely about the challenges of being an immigrant in America. The protagonist, Henry Park, who narrates the novel, never quite belongs: he was born in Korea, but lives in America, marrying a white American woman, from whom he is separated when the novel starts.
Author Chang-Rae Lee is also Korean American and is telling what has become one of the quintessential American stories, that of the immigrant experience. While there are many inspiring immigrant stories, Native Speaker tells a far more ambiguous and conflicted story. Park finds himself trapped between two worlds, belonging to neither. Although he strives to assimilate, he never is able to shed his accent and always sees himself as an outsider, something that he is constantly reminded of by the white world around him. Even his own wife, after leaving him, writes a critical note for him in which she calls him "illegal alien, emotional alien, Yellow peril: neo-American, stranger, traitor" (5).
One may be reminded of W.E.B. DuBois's concept of "double consciousness," which proposes that a non-white American is always aware of themselves as both an American and a person of color and can, therefore, never fully fit in. Park never forgets who he is. To make the point stronger, he is also an industrial spy, infiltrating the campaign of a Korean-American politician. His otherness causes him something of an existential crisis, but he also has to deal with the everyday racism of those around him, such as peers calling him "marble mouth" or "China boy."
I'm using the Riverhead Books paperback edition.