Older, but 'We Need to Talk About Kevin' by Lionel Shriver remains unmatched for its exploration of maternal ambivalence and nature vs. nurture. The darkness is so insidious because it’s framed through the mother’s retrospective, guilt-ridden letters. You’re constantly questioning her reliability and her role in shaping her son.
Is Kevin inherently monstrous, or is he a product of his mother’s coldness? The novel provides no easy answers, just a profoundly uncomfortable ambiguity. It digs into the psychology of parenting a child you fear and may not love, a theme that’s far more terrifying than any supernatural entity.