Beth's childhood is shadowed by a brutal tragedy: her brother John C. Russell Bobby killed their entire family and tried to finish the job on her. When he is caught, he is committed to a mental institution. Years later, Beth heads to college and joins a sorority. A memory lapse hides that the sorority house is really the home she grew up in, but her memories begin to creep back, awakening a sense of dread about the past.
Meanwhile, Bobby grows aware of Beth's presence and escapes the mental asylum, arming himself with a hunting knife he steals from a hardware shop.
As Beth settles into the sorority, the weekend arrivals thin the house down to just a handful of people: leaving only her, Linda Linda, Sara Sara, and Tracy Tracy in the house. The three roommates are joined by visitors, including John John, Craig Craig, and Andy Andy, who recount the old murders and add to the tension in the air.
John Vinnie Bilancio tells Beth the story of her family’s killings, which unsettles her and triggers a nightmarish recall. She wakes from a nightmare with the sense that Bobby has somehow found his way back. The memory of a knife hidden in the fireplace surfaces, and when the group investigates, they indeed find the weapon waiting in the ashes. Andy’s nerves finally snap, and he bolts for the door, only to come face to face with Bobby and be stabbed in a brutal confrontation.
Linda helps Beth confront the storm of memories, and Beth begins to piece together what happened to her years earlier. The two of them, along with Sara and Tracy, become targets as Bobby strikes at them in the house. The attack erupts outside when Tracy and Craig head to a makeshift tipi they set up earlier; Bobby rips through the shelter, stabbing Tracy to death. Craig rushes back inside to warn the others, but the lines to the outside world are dead.
Inside, Linda and Sara attempt to call the police, only to discover the telephone lines cut. Beth and John, worn down by fear, have fallen asleep, leaving the house vulnerable. Bobby finally corners Beth, and the others awaken just in time to witness the horror: John is murdered in the chaos.
Desperate, the survivors barricade themselves in a room. Craig makes a perilous escape through a window on a safety ladder, holding it for Linda to climb down. Bobby ascends the ladder, stabbing Craig to death before he can reach the ground. Linda slips back inside to safety as the ladder is removed, leaving Bobby to fall briefly as if defeated—though he is very much alive.
Thinking the danger is over, the girls attempt to flee, only to discover Bobby has somehow survived and re-enters the house to pursue them again. Beth and Linda flee, but Bobby closes in, stabbing Sara. A search party realizes he will likely return to his old house, and they rush to summon the police.
Beth and Linda descend into the basement, where Beth finally confronts the full truth of what happened to her younger self. Bobby attacks once more, and Linda swings a shovel at him, hoping to end the nightmare. The assumption that he is dead proves premature, as he stabs Linda in retaliation. Beth summons every reserve of strength, overpowers Bobby, and drives a fatal stab into his neck, ending his reign of terror. The police arrive just as Beth is escorted away, and she is taken to the hospital, where she continues to endure nightmares about her brother.
