Sadie, deeply in love with her boyfriend Kevin, plans a romantic weekend at a lake house to rekindle their relationship. Upon arriving, she discovers text messages on Kevin's phone, revealing that he has been having an affair with her best friend, Jennifer. Devastated and enraged by the betrayal, Sadie decides to confront Kevin with her findings. However, what begins as a confrontation quickly spirals into a nightmarish situation as Sadie's emotional state fractures, and she becomes unpredictable.

Sadie's anguish transforms into relentless vengeance. Her desperation drives her to take drastic measures to make Kevin and Jennifer pay for their perceived transgressions. Over the course of the weekend, psychological and physical torment ensue within the confines of the isolated lake house. Sadie's escalating actions place both Kevin and Jennifer in increasingly perilous situations, revealing the lengths she is willing to go to exact her retribution. As tensions reach a fever pitch, the situation threatens to boil over into irreversible consequences.