It is the end of the second World War and newsreel footage shows us the troops returning from Europe onboard the Queen Mary.
In a letter dated March 12, 1945 and sent to her lover abroad, a woman named Rosemary writes that she can no longer wait for him. She tells him that so much has happened and that perhaps they can be friends upon his return.
On the evening of June 28, 1945 in the small seaside New Jersey town of Avalon Bay, the townspeople hold it's graduation dance. G.I.s escort their girlfriends to the ball. Inside, the class of '45 are swinging to the orchestra's music.
Rosemary (Joy Glaccum) is attending with her new boyfriend Roy (Timothy Wahrer). The two decide to go off by themselves and drive to a lake where they spend some romantic time together in a gazebo. Lights are strung up around the gazebo and along the small nearby walk-bridge. Ominously, someone approaches the couple and cuts the power. The stranger is wearing full combat gear and carrying a pitchfork. As Rosemary and Roy embrace, she looks up and sees the pitchfork over them. Rosemary screams and the stranger plunges it through the both of them...and then leaves a long-stemmed red rose in the dead woman's hand. The revelers are oblivious back at the dance.
35 years later. The town prepares for its graduation dance once again. There hasn't been one since that fateful night. Pam MacDonald (Vicky Dawson) stops by to see Sheriff George Fraser (Farley Granger) and they discuss the event. The discussion turns to the invalid Major Chatham (Lawrence Tierney), a fellow World War II veteran, over his refusal to allow the annual celebrations after the murders all those years ago. Sheriff Fraser tells Pam that someone has robbed a store in the nearby town of Columbus and then cut up a kid and took his car.
Authorities there are afraid the killer is headed towards Avalon. Despite that possibility, the sheriff is leaving town to go fishing. He puts Mark London (Christopher Goutman), his deputy, in charge. Before Sheriff Fraser takes off, he stops by a convenience store owned by Pat Kingsley (John Seitz). One of the employees is Otto (Bill Hugh Collins), a strange "slow" fellow whom the sheriff seems to mistrust.
Pam and Mark have an attraction for each other and go on a lunch date. She shows him an article she wrote about the return of the graduation dance and tells Mark she's concerned about his safety. Pam also tells her roommate Sherry (Lisa Dunsheath) that she's worried about the Columbus killer. Sherry tries to calm her friend's nerves while the other girls in the dormitory are excitedly preparing for the dance. Lisa (Cindy Weintraub) even flashes Major Chatham, who's sitting in his wheelchair in the house across from them.
As Pam is putting the finishing touches on her outfit, someone else is getting ready too. But this person is putting on a military combat uniform, complete with a bayonet, hunting knife, and a sawed-off double-barrelled 12-gauge shotgun.
Sherry gets into the shower, and before Pam heads out, she asks Sherry if she should wait. Sherry tells her to leave because she's waiting for her boyfriend Carl (David Sederholm). When Carl shows up, he surprises Sherry in the shower. Hoping to have a little fun before they leave, he goes into the bedroom to undress. Suddenly, an intruder grabs him from behind and plunges the bayonet through Carl's head until the other end comes out of his neck. The force is so great that the victim's eyes roll back into his head. Sherry is still in the shower when she sees someone through the curtain approaching. She thinks it's Carl... until the killer (wearing a military helmet and with a gas mask covering his face) pulls the curtain open and is holding a pitchfork. As Sherry screams, he lunges it under her breasts. He then lifts her up as he sticks the pitchfork in further killing her.
At the party, Pam is happy to see Mark when he arrives. But before she can talk to him, Lisa pulls him away to dance. Pam stands by the cocktails, frustrated and annoyed. When Mark comes over to talk to her, Lisa follows him. Tipsy from the alcohol, she knocks into him and he spills some liquor on Pam's dress. Pam is furious and heads back to the dorm to change her outfit.
When Pam gets to her room, she hears the shower running. Still thinking that Sherry is in the shower, she closes the door. Little does she know that Sherry is dead and that the killer is still in the bathroom. The room is dark enough that she doesn't see Carl's blood on the bed. She changes and then leaves. But as she's going down the stairs, she hears something. Pam looks up at the top of the stairs and sees a dark figure... what looks like a G.I. wearing a gas mask. She gets creeped out and runs through the dorm.
There's no one around and just as the killer comes near her, Pam makes it outside. She knocks right into Major Chatham in his wheelchair, who grabs her arm. She breaks free and finds Mark. When she tells him that someone has been chasing her, he takes his flashlight and searches around the dorm. Mark doesn't find anything besides wheelchair marks on the ground which lead to the sidewalk.
He returns to his car where Pam is waiting for him - and she tells him to check the dorm because Sherry and Carl are still in there. Mark goes inside and towards the bedroom but the door is locked. He doesn't see that there are two dead bodies in the tub.
Pam and Mark go to Major Chatham's house. It's dark and the old man is nowhere to be found. The killer is in the house and he watches them from an upstairs window. During their search, Pam finds an old scrapbook and discovers that Chatham's dead daughter's middle name was Rosemary. She was the girl killed 35 years ago.
The two then go back to the dance, where they tell Miss Allison (Donna Davis) about the prowler on the campus. The teacher tells the students they should stay put and not go out until the person has been apprehended. That message comes too late for Lisa.
Angry that her date Paul has been puking in the bathroom, she's gone to the pool for a late night swim. After doing a few laps, Lisa ascends the stairs of the pool to go back to the party. The killer is standing above her and kicks her in the face. Shocked by the attack, Lisa tries to swim away but is unable to get her bearings. The killer then jumps into the pool, comes up from behind her, takes his bayonet... and slices her neck. Her body falls lifelessly to the bottom of the pool.
Paul wants to leave the dance and find Lisa but the teachers won't let him. He's so drunk and rowdy that he gets thrown out. Mark and Pam take him to the police station house, where Mark puts him in a jail cell.
Meanwhile, Mr. Kingsley organizes an armed posse of several men to search the neighborhood for the prowler. Otto is given a rifle and invited to come along with them.
Told that the local cemetery has been desecrated, Mark and Pam head out to see what's happened. When they get there, they find Rosemary Chatham's grave dug up. They open the coffin and find Lisa's body in it.
Meanwhile, Miss Allison has left to see if she can find Lisa. She sees blood in the pool and panics. As she tries to run away, the killer grabs her and thrusts the bayonet into her neck.
Mark tries to reach Sheriff Fraser at the lodge he's staying at but can't get in touch with him when the overweight and lazy front desk clerk refuses to place a call to his cabin, claiming that the sheriff is not there. Before heading back to Major Chatham's house, Mark tries to drop Pam off at the dance. She refuses and insists on going with him. When they get to Major Chatham's house, Mark leaves her for a moment and is knocked unconscious by the killer.
Pam spies a necklace dangling from inside the fireplace and tries to pull it out. Still in her graduation dance dress, Rosemary's skeleton falls out of the chimney. Pam tries to find Mark but is confronted by the killer. She runs through the house trying to get away and hides under a bed. The madman is now in the same room. Pam makes every attempt to be still... even as a rat comes near her. Finally, Pam gets up and runs out of the room. She manages to get the pitchfork away from the killer and holds it up for protection as he comes near her.
Just then, Otto, the clerk from Kingsley's convenience store, enters the room and shoots the prowler with his hunting rifle. Seconds later, the killer takes out his double-barreled shotgun and shoots Otto in the chest who falls dead. As the killer reloads the shotgun to shoot Pam, she stabs the prowler in the back with the pitchfork and they struggle for the shotgun. The wounded murderer pulls his mask off and Pam is horrified to see who it is. It's been Sheriff Fraser all along. Pam gets the upper hand, points the shotgun at his head and fires... exploding it to bits.
The next morning, Pam returns to the dorm, she goes into the bathroom in her bedroom and opens the shower door. The shower is still running and Sherry's body is still on the floor of the tub and Carl is hanging from the shower head by his tie. Suddenly, Carl's corpse reaches out to grab her. She screams and the screen cuts to black.