The narrator in Viet Thanh Nguyen’s stunning debut novel, The Sympathizer (Grove, $26) is a double agent, working both sides in the closing days of the Vietnam War.  A South Vietnamese Army officer educated in the West, he’s fluent in American English and culture and serves as the perfect guide for this story, noticing the hypocrisy and absurdity of U.S. involvement in Southeast Asia.  Later, called upon to be the technical advisor on a film reminiscent of Apocalypse Now, he vainly and hilariously tries to indicate the cultural stereotypes and the dehumanizing racism to the auteur director.  When a friend back in Vietnam is threatened, he returns to his country and is forced to tell his long and complicated story—to his own great peril but the delight of readers of the novel.