The novel revolves around the life of Thomas (Tommo) Peaceful as he recounts his memories. Tommo has two older brothers. His oldest brother, Big Joe, has damage to his brain and so suffers from some developmental delays but is a kind person who loves animals. His second-oldest brother, Charlie, is an intelligent man and a person of integrity who makes a number of decisions that preserve the weak and anger the strong.
Tommo is also infatuated with Molly, one of his classmates. Tommo, Molly, and Charlie grow up together and have a number of adventures, including confronting their great-aunt (known as the 'Wolfwoman') and being some of the first people in their village to ever see an airplane. However, as time goes on, Thomas begins to feel isolated and excluded due to the growing connection between Molly and Charlie, who fall in love. He later discovers that Charlie and Molly were dating in secret and that she has ended up pregnant. Charlie and Molly marry; Tommo is heartbroken but maintains his connection to them both.
Soon, World War I arises and Charlie and Thomas are enlisted to fight in the war. Tommo tells the stories of his wartime experiences, including his training and the savage trench battles he endures in France. Eventually, the brothers come under the command of the cruel Sergeant Hanley, who harbors a strong dislike for Charlie. Throughout this time, Charlie protects Thomas from the worst of the cruelty of the war.
During one of the attacks, Tommo becomes injured in No Man's Land. Charlie refuses to leave his brother when Sergeant Hanley orders the men to run back into combat. Charlie also tells Hanley that this order is suicidal and that men will die carrying it out. Hanley says that he is refusing a direct order to fight in the war effort and therefore is guilty of desertion—even though Charlie is right and most of the men who follow Hanley's charge end up dying. Hanley survives, however, and charges Charlie with the crime of desertion. After a very brief trial in which Charlie is given little opportunity to defend himself, he is executed. His brother Tommo maintains an all-night vigil and listens to the gunshots of the firing squad that kills his brother.
Thomas endures the remainder of the war and comes home to Molly and her child, "Little Tommo," with the goal of spending his life caring for them in honor of Charlie's memory.
