Beginning with O'Brien lying in a ditch next to his buddy Barney, the narrative introduces the audience to a chaotic environment. O'Brien is a soldier in Vietnam, a tragic fate because he never supported the war to begin with. The opening focuses upon the intense horror of the conflict. Anxiety, fear, and disorientation do not change throughout subsequent battles because the fear of death is constant the entire time O'Brien is overseas.
O'Brien grew up in Worthington, Minnesota. He remembers his family possessing a strong patriotic bent, and war was an active part of his childhood because his town had sent many soldiers to the Korean War already. In high school, O'Brien fundamentally opposes the Vietnam War. He cannot justify the loss of life. He decides to run away to Canada to avoid the draft, but he gives up at the last second and attends his draft. At Fort Lewis he becomes friends with Erik, a fellow anti-war activist. Although they are mistreated for their pacifist stance, these two survive basic and are set to deploy to Vietnam.
O'Brien makes plans to escape to Canada and Sweden, but ultimately he concludes he cannot run away from this problem when so many others are actually unable to run away at all. O'Brien serves in Alpha Company in Landing Zone Gator under Captain Johansen. His service is dramatic, terrifying, and constantly changing. O'Brien never remains in one place long. In addition to this he's profoundly alone, as he cannot allow himself to grow close to fellow soldiers because everyone around him is constantly dying. Morale is the real mission.
By a strange twist of fate, O'Brien is moved to an investigative command outside the combat zone. He works under Major Callicles who is investigating legal concerns in the My Lai Massacre. Although Major Callicles is strict, he is determined to conduct his investigation thoroughly and by the book. O'Brien observes how the heavy discoveries of corruption and misinformation in the U.S. military's conduct take their tole on the major. Finally, one day, O'Brien is dismissed and flown home. Back home, he feels no pride or satisfaction, only depression. He and all of his fellow veterans now face the moral weight of having participated in a cause for which they always had felt reticent, only now they have killed people and survived. O'Brien feels guilt for having survived. He also feels like a victim of greedy government bureaucracy.
