The unnamed narrator is a mole for the Communist North in the South Vietnamese military. Unlike a lot of spy novels, the tension in this book is all about the narrator trying to be two different moral people, not a spy who tries not to be discovered. As a mole, he does terrible things to people on both sides of the conflict. He is also the son of a French man and Vietnamese woman, which brings its own tension. After they evacuate and become refugees in the U.S., he has to negotiate between being Vietnamese and American expectations and views. All of these pull him in brilliantly written fashion in multiple directions. It's rare that I get this engaged with a book where the tension is primarily internal, but it pulled me in so much I missed a Muni stop even. There's a few scenes of action, but the tough stuff is in our protagonist's inner monologue.

@sanae@bookwyrm.social has a much meatier review of The Sympathizer than mine; go read their review for a deeper discussion of the book's ethics.