Kevin Katchadourian killed seven of his fellow high-school students, a cafeteria worker and a teacher, shortly before his sixteenth birthday. He is visited in prison by his mother, Eva, who narrates in a series of letters to her estranged husband Franklin, the story of Kevin's upbringing. A successful career woman, Eva is reluctant to forgo her independence and the life she shares with Franklin to become a mother.
Once Kevin is born, she experiences extreme alienation and dislike of Kevin as he grows up to become a spiteful and cruel child. When Kevin commits murder, Eva fears that her own shortcomings may have shaped what her son has become. But how much is she to blame? And if it isn't her fault, why did he do it?