"They were said to have soldier's heart," says Paulsen of Civil War veterans such as Charley Goddard. Nowadays the term is post-traumatic stress disorder. The novel is a psychological study focused on the mind of a teenager who lied about his age and enlisted in the Union army. Charley is fifteen years old when he enlists. His reasons are foolish: He hears that the war may be the only one to come in a lifetime and that it would be a shame to miss it. Besides, "It would be over by fall," he hears.

He seems to be a good kid. He is tall, with big hands, and a hard worker on the family farm. Yet, he is naive and unworldly. His mother sees him off but soon regrets her decision. Charley undergoes what seems to be standard training—a boot camp of drills and...