In the late 1980s, a shy and awkward boy named Jeremy Melton is brutally rejected and humiliated by a group of popular girls at a junior high school Valentine's Day dance. Fast forward to the present day, those same girls, now grown women, are friends navigating their professional and personal lives. Shelly, Paige, Kate, Dorothy, and Lily each receive disturbing Valentine’s Day cards from an anonymous sender, leading them to suspect that someone from their past may be seeking revenge. Shelly is soon found murdered, leading the group to realize they are being targeted.

The women grow increasingly paranoid as they are stalked and terrorized by a mysterious masked figure. Old secrets and recriminations resurface among them, intensifying the sense of dread. As the stalking escalates, each friend is forced to confront their own past actions and relationships. They begin to question everyone around them, including old flames and new acquaintances, in an effort to unmask their tormentor before it's too late. Meanwhile, Detective Vaughn conducts an investigation, but his involvement complicates their trust issues further. The tension peaks as the friends strive to survive this meticulously planned vendetta.