At Hamilton High School's 1957 prom party goers Lisa and Brad leave the festivities to have sex in Brad's car. Before the two can undress, they are distracted by a noise, revealed to be someone putting candles on the hood of the car. After spotting the candles, Lisa has her throat slashed by a metal crucifix wielded by psychotic religious fanatic Father Jonas who also stabs Brad in the chest, afterward disposing of the teens' bodies by blowing up Brad's car. After committing this double homicide, Father Jonas, revealed to have stigmata, is transported from St. Basil Seminary to the St. George Church by a group of fellow priests led by Father Jaeger, who refers to the rambling Father Jonas as an abomination and believes him possessed by dark forces.
In 1991 at St. George Church young Father Colin is informed by the now elderly Father Jaeger that his trip to Africa for missionary work has been put off and that he has been charged by the church with watching over Father Jonas, who has been captive in the church basement for thirty-three years in a drug-induced stupor; shortly after showing Colin the catatonic Jonas, Jaeger passes away, officially leaving Colin as Jonas’s new guardian. Jonas reveals that he had suffered sexual abuse from priests in the church. Believing he can help Jonas, Colin neglects drugging him, an act which allows Jonas to regain consciousness, escape his bonds and kill Colin by garroting him before taking off to St. Basil Seminary, hitching a ride with a trucker named Dave, who he kills afterward. Discovering Colin's death and Jonas's escape, Cardinal Tourette makes Colin's murder look like a suicide before going off in search of Jonas.
At the St. Basil Seminary, which has long since been abandoned and converted into a summer home, two young couples - consisting of the summer home owner's son Mark, his good girlfriend Meagan, the mischievous Laura and her boyfriend Jeff - arrive planning to celebrate their graduation privately instead of going to prom, but find most of the electronics and appliances in the house have been stolen. Deciding to stay and still party, the group is stalked by Jonas, who acquires his old metal crucifix and uses it to kill Mark's younger brother Jonathan, who had followed the group to the house and was in the midst of secretly filming Jeff and Laura having sex before being murdered.
After injuring herself in the wine cellar, Meagan receives an obscene phone call from Jonas while Mark is away getting the first aid kit to tend to her wounds. After calling Meagan, Jonas enters the house through his old lair and kills Laura, subsequently moving her body. While looking for the missing Laura, Mark and Meagan find Jonas's lair, while Jeff searches the attic. Finding what looks like Laura, Jeff approaches the figure, only to find it is Jonas wearing Laura’s scalp; Jonas proceeds to kill Jeff by crushing the boy's skull with his bare hands.
Going outside to look around, Mark and Meagan rush back inside when they find Laura and Jeff's bodies crucified and ablaze. As Meagan tries to call the police Mark arms himself with a gun and has Meagan flee outside when Jonas appears. Rushing to the roof of the house, Mark is stabbed in the foot through the roof by Jonas, causing him to fall to the ground below. After Jonas finishes off Mark by hurling his crucifix into the boy's chest, Meagan is stalked through the house by the fanatic, who she manages to briefly incapacitate by spraying him in the face with bug spray. Going outside and getting Mark's earlier dropped gun, Meagan gets bullets from inside and, after being phoned by the police (a call which is interrupted by Jonas) goes to the wood shed outside. After missing several times Meagan manages to shoot Jonas and, believing him dead, begins praying for forgiveness, only to be attacked mid-prayer by the still living Jonas, who begins setting the barn on fire. Grabbing a shovel, Meagan beats Jonas with it and rushes outside and locks the door, leaving Jonas to burn and subsequently be blown up when the shed explodes.
In the morning Meagan is loaded into an ambulance, while the charred and seemingly dead Jonas is placed in another, which is manned by Cardinal Tourette and his followers. While in the back of the ambulance, Jonas opens his eyes, while elsewhere Meagan does the same simultaneously.Nicole de Boer as Meagan
J.H. Wyman as Mark
Joy Tanner as Laura
Alle Ghadban as Jeff
Kenneth McGregor as Jaeger
Brock Simpson as Father Colin
James Carver as Jonas
Krista Bulmer as Lisa
Phil Morrison as Brad
Fab Filippo as Jonathan
Thea Andrews as Louise
Deni DeLory as Jennifer
In a retrospective assessment of the film, critic Thomas Waugh noted that the film "milks in its own way the then recent but in fact perennial abuse scandals in the Catholic church." Chris Parry of eFilmcritic.com said the film "beats the tar out of the second and third films in the Prom Night series, but that's kind of like beating a wheelchair kid with a rake; though it might be fun for a moment or two, it's hardly a landmark achievement."