A group of former high school students receives mysterious invitations to a ten-year class reunion at their now-abandoned high school. Among these individuals is Marty, a nerdy outcast who had been severely bullied by this same group during their school years. The flashback to their school days reveals that a cruel prank turned horribly wrong, leaving Marty disfigured and emotionally scarred. The former classmates, blissfully unaware of the host’s true identity and motives, decide to attend the reunion out of curiosity.

As the night progresses, the attendees find themselves locked inside the decaying building, realizing that the reunion was a trap set by someone who holds a deadly grudge. Their joyful reminiscing quickly turns into a frantic fight for survival as they are picked off one by one through a series of gruesome, elaborate traps that reference their past sins. Tensions rise as they try to remember what they did to deserve such retribution while desperately searching for an escape.