Eva Khatchadourian, once a celebrated travel writer, now resides in a dilapidated house and works at a travel agency situated near a prison. Here, she makes frequent visits to see her son Kevin, who is incarcerated for the horrific act of mass murder against his high school classmates. As she navigates the hostility from her neighbors, Eva is often lost in thoughts about the memories of raising Kevin.
Though hesitant to embrace motherhood, Eva ultimately commits to starting a family with Franklin by having Kevin. From a young age, she perceives Kevin as emotionally distant and challenging. His behavior appears to be filled with disdain for her, as he deliberately strives to provoke her. His infancy is marked by constant crying, but notably, he only exhibits this behavior around Eva. In his early years, he resists her efforts at toilet training, rejects her affection, and shows apathy toward everything that surrounds him. Conversely, he presents a facade of a loving child to his father, Franklin, who casually dismisses Eva's concerns and offers excuses for Kevin's troubling actions.
One day, frustration overwhelms Eva, leading her to angrily throw Kevin against the wall, which results in a broken arm for him. Kevin cleverly spins the tale to Franklin, claiming he fell, thereby manipulating Eva’s reputation further.
During a moment of illness when Kevin is confined to bed with a fever, he surprisingly shows affection for Eva as she reads him the tale of Robin Hood. However, this moment is fleeting, as his spiteful tendencies swiftly return upon recovery. Franklin showers Kevin with gifts like a bow and arrow, teaching him archery as a bonding activity.
Later, Eva gives birth to a second daughter, Celia, a bright and delightful child, whom Kevin regards with immediate contempt. As the years pass, tragedy strikes when Celia’s pet guinea pig mysteriously disappears, only for Eva to discover its remains in the garbage disposal the following day while attempting to unclog it. During this incident, Celia suffers an injury to her eye due to exposure to drain cleaner, which Eva suspects Kevin may have intentionally caused. Despite Eva's growing suspicions about her son's role in the incident, Franklin remains in denial, which strains their marriage and leads him to contemplate divorce. Kevin eavesdrops on their conversation, deepening the chasm of mistrust within their family.
On the cusp of turning 16, Kevin commits the unimaginable; using bicycle locks, he traps several of his peers in the school gymnasium and heinously murders them with a bow and arrow. Witnessing the aftermath of Kevin's arrest and the grim procession of his victims raises unspeakable horror within Eva. Upon returning home, she discovers that both Franklin and Celia have been brutally slain by Kevin.
Two years following the massacre, Eva pays a visit to Kevin in prison. Notably, she sees a different side of him—one that appears demure and fearful, as he anticipates his transfer to an adult facility. With a heavy heart, she quietly asks him why he carried out such horrific acts. Kevin responds thoughtfully, confessing that he once believed he understood his motivations but is now engulfed in uncertainty. In a final wave of emotions, Eva embraces Kevin before parting ways, leaving both haunted and searching for answers.
