College students Vivia, Jennifer, and Phoebe decide to pledge a sorority at their university, Briggs College. During hell week, the sorority's housemother, Mrs. Henshaw, urges the women not to hold their initiation rituals at Pratt House, an abandoned fraternity nearby. Mrs. Henshaw goes to Pratt House and, in an overgrown garden outside, visits the tombstone for a man named Allan. She implores that, should the students do enter the house, that Allan leave them alone. Upon going inside, Mrs. Henshaw is bludgeoned to death by an unseen assailant.
The day of the initiation, Vivia, Jennifer, and Phoebe break in to a fraternity to steal clothing as part of their hazing ritual. Inside, Jennifer is confronted by Blake, who swiftly takes romantic interest in her. Back at her dorm, Jennifer is met by her shy classmate Martin, who returns a book she dropped outside. That night, the women arrive at Pratt House for their hazing ceremony. During the hazing, which includes the women be forced to hold raw eggs in their mouths, the lights begin to flicker, and the group are terrified when glasses begin flying off a table by themselves. Vivia goes downstairs to investigate noises, and when the women follow, they find her bound to a guillotine and watch her be beheaded. Vivia suddenly emerges from the shadows and picks up the severed head, revealing the entire scenario to be an elaborate prank using a dummy.
The following morning, Martin gives the women a ride to the sorority to receive news of their acceptances or rejections. All three are selected, though Vivia learns that her prank was the only reason for her acceptance. Veronica, the sorority's leading member, demands Vivia recreate the prank during an upcoming April Fool's Day masquerade party at Pratt House. At a committee meeting for the university's Greek society, Professor Zito recalls the hazing ritual 22 years ago that resulted in Allan's death by a guillotine. That afternoon, Jennifer, Phoebe, and Vivia set up the prank in Pratt House, and Jennifer tells them she did research showing that Allan was involved in the occult and had conjured evil; she also cites news articles about people going missing in the house, never to be found. Later, Professor Zito inspects the house, and is electrocuted by an assailant in the basement.
At the party that night, Vivia's prank is hatched during Veronica's toast, and Jennifer is dragged into the basement by a hidden cord while the partygoers watch in horror. In the basement, Jennifer and Vivia laugh and quickly prepare Vivia's guillotine stunt, when Jennifer is suddenly overcome and possessed by a spirit. She returns upstairs in silence, and worriedly tells Blake she needs to leave. Vivia follows, aborting the guillotine stunt. As the party filters out, Pam, a sorority sister, is killed with a trident by someone dressed in a diving suit. The same assailant beats Veronica to death with a hammer before using the guillotine to kill Albert. Blake is subsequently lured into a bathroom. Numerous partygoers are dispatched in swift succession, and Vivia discovers the dismembered body of a delivery boy named Virgil in the refrigerator.
Vivia flees upstairs to retrieve Phoebe, and the two find Blake's drowned corpse in the bathtub. They are subsequently confronted by Jennifer, who reveals herself to be possessed by Allan. Jennifer pursues them with the trident, causing the stairs to collapse as they climb them. They attempt to escape through an upstairs window, but Jennifer throws Vivia to the ground, breaking her legs, before propelling after her. Phoebe climbs down the wall and begins beating Jennifer with a broken board before impaling her through the chest, killing her. Phoebe consoles Vivia, but it is soon apparent that she has been overtaken by Allan's spirit. Police arrive and whisk the two women away together in an ambulance, as Vivia pleads not to be left alone with the possessed Phoebe, who smiles maliciously at her. The ambulance drives away in the night, while Vivia still screams.
