During a college costume party, a bold initiation unfolds for four new pledges into Alpha Sigma Rho: Jeff Reed, who comes from a life of privilege; Marti Gaines, an intelligent girl who grew up in a poor environment; Denise Dunsmore, a party-loving girl from England; and Seth Davies, a Southern California surfer. The plan takes them to the deserted Garth Manor, a mansion once owned by Raymond Garth, who murdered his wife Lillian and their three deformed children, Morris, Margaret, and Suzanne, then hanged himself. The mansion’s grim history looms as the pledges are corralled behind the estate’s iron gates and left to spend the night on the grounds, while the legends insist Morris and Andrew still haunt the place.
The night quickly spirals into fear as Peter Bennett, who oversees the initiation, and two students, May West and Scott Zamboni, set up frightening stunts around the manor to kick off the scares. But the playful horrors take a deadly turn when May and Scott are murdered by an unseen assailant. Peter later discovers Scott’s body strung on the roof and bolts into the hedge maze, where a second attacker ends Peter’s life with a swift scythe strike.
Back at the house, Seth heads to the bathroom only to return and find Denise missing and May’s severed head laid out on a bed. Panic drives him to alert Marti and Jeff, and they scale the gates to seek help. Jeff investigates a suspicious light in the maze and finds Peter’s flashlight near his own lifeless body. A shadowy figure then attacks them in the bedroom, and Jeff wounds the intruder with a pitchfork before the assailant disappears. The trio discovers a rug is hiding a trapdoor, through which the intruder escaped. Descending into the tunnels, they uncover Denise’s body laid out beside preserved remains of Garth’s family members, a shocking tableau that confirms a more horrifying secret.
Seth, meantime, makes his way to the local police station, but the officers dismiss him as part of a fraternity prank. He steals a shotgun and carjacks a vehicle to press on. Jeff and Marti manage to elude the deformed Garth brothers, but the pursuit continues. Seth returns to the mansion and shoots Morris Garth, creating a chaotic confrontation in the foyer. Jeff and Marti confront him there, yet Andrew intervenes, killing Seth as he tries to protect Marti. They scramble to reach a window, but Jeff is thrown from it by Andrew, perishing in the fall.
Marti presses on into the hedge maze and finds Peter’s corpse, then pries the gate keys from his fingers. She unlocks the gates and escapes in Seth’s stolen car, though she must slam the vehicle through the fallen gate and continue driving. Ambushed by Andrew, she drives straight into the gate’s spikes, impaling him. Morning light washes over the mansion as Marti stumbles from the car, the ordeal behind her but the memory of the night lingering as she walks away.
