The film opens on October 31, 1963, a cold Halloween night in Haddonfield, Illinois. In the middle of a street stands a two-story white Victorian house. Someone begins walking toward it, and sees a 17-year-old Judith Margaret Myers (Sandy Johnson) through the front door, kissing her boyfriend (David Kyle) passionately. As they move towards the couch in the living room, the person outside follows them around the side of the house and watches through the window. The boyfriend asks Judith if they are alone and she replies that someone by the name of Michael is around someplace. Her boyfriend puts on a clown mask jokingly and kisses her. She laughs and tells him to take it off and he suggests that they go upstairs to have sex. They run up the staircase as the person outside the house follows them back around to the front. The Shape sees the light in the upstairs window go out and begins swiftly walking back to the side of the house through the kitchen door. Quickly, the Shape opens a drawer and grabs a very sharp knife. It begins slowly creeping through the dining and living rooms and reaches the bottom of the staircase. There, Judith's boyfriend is putting his shirt back on and leaving the house. Judith calls down the staircase for him to call her the next day. He takes one last look upward and quietly leaves. As soon as this happens, the shape begins walking up the stairs into the dark hallway. Looking down, it sees the clown mask on the floor. The Shape picks it up and pulls it over its face. Entering Judith's bedroom, it sees her sitting in front of her mirror, nude except for a pair of panties, brushing her hair. She has her back to the shape and is unaware that it is standing there. The Shape walks up behind her and she finally feels its presence. Swirling around, she sees that it is Michael (Will Sandin), the person previously referenced, and is annoyed, quickly covering her breasts. But suddenly, Michael raises the knife and begins stabbing her repeatedly in various areas of her body. After a few seconds, she falls to the ground, covered in blood. Swiftly, the shape walks out of the bedroom, down the stairs, and out the front door into the yard as a car pulls into the driveway. They are Mr. and Mrs. Myers, Judtih's parents. Seeing Michael, they pull off his clown mask, revealing the face of a young 6-year-old boy staring into space with a blank expression, still clutching the knife in one hand.
On October 30, 1978, nearly 15 years later, in Smith's Grove, Illinois, a doctor by the name of Sam Loomis (Donald Pleasance) and his assistant, a nurse named Marion Chambers (Nancy Stephens), are driving to the local sanitarium to have Michael Myers, now 21 years old and still very dangerous, taken to a hearing in front of a judge, where his future incarceration will be determined. In the car is a matchbook with an advertisement for the Rabbit in Red Lounge. As Marion quietly smokes a cigarette, she questions Dr. Loomis's desire to do this when suddenly, they see that several mental patients are lurking around the entrance to the sanitarium. Dr. Loomis rushes out of the car into the rain to see what is going on just as a patient leaps on top of the car. It is Michael Myers (now played by Nick Castle). Marion rolls down the window to see what he is doing up there and his hand reaches through the window and grabs Marion's hair, causing the car to swerve off the road. He and Marion struggle for a moment until she pulls away and moves toward the other side of the car. Instantly, Michael's hand appears at the window behind her and shatters it. Marion, startled, opens the car door and jumps out. Michael climbs in and drives away. Dr. Loomis runs over to Marion and consoles her, telling her that the evil is gone.
The next day, on Halloween in Haddonfield, a young girl about 17 years old named Laurie Strode (Jamie Lee Curtis) is leaving her house to walk to school. On her way out, her father Morgan Strode (Peter Griffith), a real estate agent, tells her not to forget to drop a key off at the old abandoned Myers house because a family is coming by to look at it later. As Laurie continues down the streets, an 8-year-old boy, Tommy Doyle (Brian Andrews), walks up to her. Laurie is babysitting him that night. As they walk together, the Myers house comes into view. Tommy tells Laurie not to go up there because something bad happened there once. As she drops the key under the mat, someone appears inside and looks through the front door at her. Laurie leaves and continues walking with Tommy, who says he received the information about the house being haunted from Lonnie Elamb (Brent Le Page), whom Laurie says will probably never get out of the sixth grade. Tommy leaves soon after this, and Laurie walks on, singing to herself, when suddenly, the Shape from inside the Myers house appears right behind, staring after her.
Meanwhile, back in Smith's Grove, Dr. Loomis is debating with another doctor, Terence Wynn (Robert Phalen), about whether or not Michael has returned to his hometown in Haddonfield. Dr. Wynn doesn't think Michael could drive to Haddonfield and blames Dr. Loomis for not warning the staff about the potential for Michael's outburst. Dr. Loomis angrily gets in his car and drives away.
Later that day, Laurie sits in English class at Haddonfield High School when she sees the Smith's Grove Sanitarium car parked on the street outside the window. Michael stands beside it, in a greyish-white mask, watching her. Laurie is frightened and continues to look back, when suddenly, the teacher calls on her to answer a question, startling her. Laurie responds to the question, and when she looks back through the window, Michael and the car have disappeared.
Meanwhile, at the Haddonfield Elementary School, the bell rings, and children begin running out of the building. Tommy is leaving school carrying a large pumpkin, followed by several bullies who are taunting him about how the boogeyman is coming to get him that night. Tommy is confused, not knowing about the boogeyman, but is also frightened. He begins to run away, but he trips and falls, squashing the pumpkin. The bullies laugh and run out through the playground gate, when instantly, Michael jumps out and grabs one of them. Terrified, the bully scurries away. Michael climbs back into the Smith's Grove Sanitarium car and begins to drive alongside Tommy, who is walking down the sidewalk sadly.
On the highway somewhere between Smith's Grove and Haddonfield, Dr. Loomis stands at a telephone booth, speaking with someone from the Haddonfield police department, who seems resistant to the idea that Michael could be coming to Haddonfield. Dr. Loomis, frustrated again, hangs up the phone. But before he can drive away, he notices a tow truck parked nearby in a grassy area. Inside, he finds Michael's white hospital gown and the Rabbit in Red Lounge matchbook. Now Dr. Loomis is sure that Michael is in Haddonfield and rushes back to his car, not noticing the unclothed body of the tow truck driver (Barry Bernardi) lying in the nearby grass.
Meanwhile, the students are being released at Haddonfield High School. Laurie is walking home with her friend Lynda van der Klok (P. J. Soles), who's complaining about how many school activities she will have to be involved with in the next day, being such a popular and beautiful girl. Laurie, however, seems to be a quiet bookworm who has nothing to do except babysit. As they walk along, another young girl named Annie Brackett (Nancy Loomis) finds them. Annie and Laurie talk about their babysitting assignments for that night; Laurie is babysitting Tommy, and Annie is babysitting Lindsey Wallace (Kyle Richards), who lives across the street a few houses away. While they are talking, the Smith's Grove Sanitarium car goes speeding down the street. Annie yells down the street at the driver that speed kills and, suddenly, the car stops but instantly speeds back up and leaves again. Forgetting this matter and not realizing that they had a close encounter with Michael, Annie and Lynda share a cigarette and begin devising a plan to get Lynda and her boyfriend, Bob, together at the Wallace house where Annie is babysitting to have sex.
Laurie and Annie continue on, when suddenly, Laurie sees Michael hiding behind a bush ahead of them. Annie doesn't see him, and when she rushes over to the bush, there is nobody there. Annie thinks that Laurie is seeing men behind bushes because she is desperate for a date. Annie reaches home, leaving Laurie behind, who still thinks that there was someone behind that bush. Looking behind her, she accidentally runs into Mr. Brackett (Charles Cyphers), Annie's father and the sheriff of Haddonfield. Laurie is startled, and Brackett , the local sheriff, replies that it is Halloween and everyone is entitled to one good scare. Laurie laughs and walks back towards her house. Walking into her bedroom, she looks out of the window and sees Michael standing in her neighbor's back yard, staring up at her from between two rows of clothes hanging on a line. One minute he is there, the next minute he is gone. Suddenly, the phone rings, and Laurie runs over to it. When no one answers and she only hears the sound of chewing, she hangs up, terrified. The phone rings once again and it is Annie on the other end. She asks why Laurie hung up on her and she replies that she thought it was an obscene phone call. Annie says that she had her mouth full and couldn't speak, telling Laurie that she will be picking her up for their babysitting assignments at 6:30. Laurie hangs up and lies on her bed, trying to console herself. Later that day, Annie picks Laurie up at her house to go babysitting, and they drive around for a while smoking a marijuana cigarette.
Meanwhile, Dr. Loomis arrives at the Haddonfield Cemetery with the graveyard keeper (Arthur Malet), apparently with the intent to visit Judith's grave. They discover that Judith's headstone is now missing; Dr. Loomis knows now there can be no doubt that Michael is somewhere in Haddonfield.
Back in Annie's car, the girls smoke marijuana and talk. Laurie tells Annie about seeing someone in her neighbor's back yard, while behind them the Smith's Grove Sanitarium car slowly cruises down the road, stalking them. Laurie begins to cough after smoking the marijuana when suddenly, they spot Mr. Brackett in front of a store in the distance and Annie orders Laurie to get rid of the joint. They pull into the parking lot and speak with Mr. Brackett, who says that someone--probably kids--broke into the store and stole a few masks, ropes, and knives. Annie replies that he blames everything on kids and that he is a cynical father. Mr. Brackett dismisses them because they will be late, and they leave down the street toward their baby-sitting assignments. After they leave, Dr. Loomis pulls up to the store and asks to speak with Mr. Brackett, who says it will be about ten minutes. Dr. Loomis stands waiting on the sidewalk as the Smith's Grove Sanitarium car passes right behind him.
In Annie's car, Laurie is worried that Mr. Brackett knew that they were smoking pot, and Annie thinks there is nothing to worry about. They begin discussing the school dance the next day, and Laurie reveals to Annie that she has a crush on a boy named Ben Tramer. Soon after this, they arrive at their destinations. Annie drops Laurie off at the Doyle house and pulls into the driveway of the Wallace house. As she walks into the house, the Smith's Grove Sanitarium car pulls up and Michael hides behind a tree in the Wallace yard, watching Annie.
Meanwhile, Dr. Loomis and Mr. Brackett arrive at the Myers house. They begin to search inside, when they find a partially eaten dog. Mr. Brackett says a man couldn't eat a dog like that, and Dr. Loomis replies that this isn't a man. The two of them walk upstairs, and Dr. Loomis shows Mr. Brackett the bedroom where Judith was murdered. Suddenly, a downspout falls away from the building and breaks the window near them, startling Dr. Loomis, who draws his gun. He begins describing his 15-year experience of watching Michael, seeing nothing but pure evil inside him. Mr. Brackett asks what they should do, and Dr. Loomis tells him to inform the rest of the police, just to ask them to keep their mouths shut. Dr. Loomis decides to stay behind and wait for Michael because he thinks he will return to the Myers house.
At the Doyle house, Laurie sits, reading King Arthur to Tommy. Tommy becomes bored and says that he doesn't like that book and reveals several comic books that he has been hiding in the couch, saying that his mom doesn't want him to read them. Soon after this, Tommy asks Laurie what the boogeyman is, but suddenly, the phone rings before she can reply. It is Annie, calling from the Wallace house. She tells Laurie that she just spoke with Ben Tramer and told him that Laurie was really attracted to him. Laurie becomes angry and embarrassed, and begs Annie to say that she didn't talk to him. Right at this moment, Tommy looks out the window and sees The Shape standing next to the Wallace house, a black silhouette. He screams for Laurie that the boogeyman is outside, but when Laurie looks out the window, no one is there, and she continues her conversation on the phone. At this time, Michael has reached the back of the house near the kitchen door. Inside, Annie is in the kitchen making popcorn, not noticing Michael. She complains about Lester, Lindsey's dog, bothering her with his barking. Suddenly, Annie accidentally pours the butter all over her shirt and pants, and removes them while Michael continues to watch. Annie finds a small button-up shirt and puts it on, wearing nothing else other than panties. At this moment, Michael accidentally knocks a hanging plant to the ground, shattering it and drawing Annie's attention to the kitchen door. But Michael has gone to another window when Lester, who is now outside, sees him and begins barking. Annie complains to Lindsey again that Lester is getting on her nerves, but soon after this, she hears Lester stop barking and begin whimpering. Outside, Lester is dangling in the air and his feet are starting to go limp as Michael kills him.
Inside the Doyle house, Laurie and Tommy sit watching The Thing. Once again, Tommy asks Laurie about the boogeyman. Laurie says that the boogeyman and all other Halloween superstitions are all make-believe and that Halloween is only a time when people play tricks on each other. Seeing that Tommy's still afraid, Laurie promises that she won't let anything happen to him. Tommy asks to make the jack-o-lantern at this time and they go into the kitchen. At the Wallace house, Annie goes to the outdoor laundry room in the back yard and puts her clothes in the washing machine, never seeing The Shape peering in at her from the door and windows. After accidentally locking herself inside, Annie calls for Lindsey to come and let her out, but Lindsey doesn't hear her. When the phone rings, Lindsey answers it and it's Annie's boyfriend, Paul. Lindsey finds Annie stuck in the laundry room window and releases her. After they go back into the house, Paul calls again and tells Annie that his parents left his house and he has an opportunity to sneak out to see her. He asks her to come pick him up. Annie takes Lindsey across the street to the Doyle house so Laurie can watch her for the time being. Laurie is reluctant, but Annie promises to talk to Ben Tramer in the morning and tell him that they were just fooling around when she called him. Finally, Laurie agrees, and Annie goes back to the Wallace house. She enters the garage, whistling and singing to herself, and tries to open her car door, but it is locked. Frustrated, Annie goes back into the house and finds the keys, brushing her hair a bit in the mirror, and still wearing nothing underneath her coat except a shirt and panties. Reentering the garage, she opens the car, not noticing that it is now unlocked. Just as she sits down in the driver's seat, she realizes what has just happened. She reaches up to wipe the fog from the windshield, when suddenly, Michael leaps out from the back seat and grabs her throat. He mercilessly strangles her until she weakens and then swiftly withdraws a knife and slits her throat. Annie's eyes go wide as her face slides down the window, and she dies.
Inside the Doyle house, Tommy and Lindsey are watching television when Tommy hides behind a curtain and whispers Lindsey's name, trying to scare her. Tommy turns around, and, to his horror, he sees Michael carrying Annie's lifeless body back into the Wallace house. Suddenly, Lindsey bumps into Tommy and they both scream. Tommy yells for Laurie, saying that they boogeyman is outside again, but she tells him to stop talking about it. Tommy complains that no one believes him, but Lindsey decides that she will.
Meanwhile, at the Myers house, Dr. Loomis stands waiting behind a bush. After a while, three children, one of whom is Lonnie Elam, come along and dare each other to go inside. Trying to protect them, Dr. Loomis speaks in a menacing tone and yells at them to go away. They scurry away from the house and run down the street. Suddenly, Mr. Brackett jumps out behind Dr. Loomis, startling him. Mr. Brackett complains, telling Dr. Loomis that it will take more than fancy talk to keep him up all night crawling around bushes. Dr. Loomis warns him once again of Michael's evil, and Mr. Brackett questions if all the families and children in Haddonfield could be lined up for a slaughterhouse. Dr. Loomis replies that they could be. Mr. Brackett agrees to continue looking for Michael in the case that Dr. Loomis is right, but he adds that if he is right, "Damn you for letting him go."
Back at the Wallace house, Lynda and Bob arrive, both sipping from cans of beer and are considerably drunk. They go over the plan that Annie will distract Lindsey while they go to the bedroom upstairs to have sex, not knowing that Lindsey is at the Doyle house and that Annie is dead. Bob lifts Lynda into the air and carries her into the house. Once they go inside, they find all the lights off and no one there. Seeing this as an opportunity, they fall onto the couch, kissing passionately, while Michael silently watches nearby.
At this time, in the Doyle house, Laurie, Tommy, and Lindsey have finished carving the jack-o-lantern and walk into the living room, making spooky noises. They all sit down on the couch to finish watching the movie, when suddenly, the phone rings. It is Lynda calling from the Wallace house while lying on the couch with Bob's head in her lap. She asks where Annie is; Laurie replies that she went to pick up Paul, and she thought she'd be home by this time. Laurie tells Lynda to call when Annie gets back because she has Lindsey at the Doyle house, and she needs to know what time to put her to bed. Enthusiastically, Lynda hangs up the phone and tells Bob that Lindsey is gone for the night, and they run upstairs. Laurie watches as the lights go out across the street.
Upstairs in the Wallace house, Lynda and Bob Simms (John Michael Graham) are having sex while the phone rings continuously. Lynda warns Bob not to answer it for fear it might be the Wallaces. Bob takes the phone off the hook and they resume the moment, not noticing Michael's shadow sliding across the wall. Soon after this, they stop, and Lynda lights a cigarette for each of them, ordering Bob to go downstairs for a beer. She giggles as he goes downstairs, this being the best night of her life. Downstairs, Bob gets two beers out of the refrigerator and is about to pour them into glasses when he hears a noise. He looks outside through the kitchen door, but no one is there. Annoyed, he opens the pantry door when suddenly, Michael jumps out and shoves him against the set of cabinets on the opposite wall! Michael lifts Bob into the air, stabs a sharp knife through his stomach and into the wall, and Bob dies. Michael stands there for a moment, watching Bob's lifeless body like a curious animal. Upstairs, Lynda sits filing her nails when the bedroom door creaks open and Michael stands there, covered with a sheet and Bob's glasses over his eyes. Lynda thinks this is Bob dressed as a ghost and asks him where the beer is. He won't answer, so she drops the sheet around her, exposing her breasts. When the Shape still won't answer her, she becomes annoyed and gets up to call Laurie and ask where Annie and Paul are. She dials the number, but just as she is about to speak, Michael comes behind her and strangles her to death with the telephone cord! At which time she screams, leaving Laurie thinking it is Annie playing a prank. Finally, after Lynda dies, Michael picks up the phone, listening to Laurie's voice. She puts the phone down and looks out the window, she dials the number for the Wallace house, but no one answers. Going upstairs, Laurie sees that Tommy and Lindsey are sound asleep.
Meanwhile, back at the Myers', Dr. Loomis still stands waiting, when suddenly, he sees the Smith's Grove Sanitarium car! Dr. Loomis begins running down the street, sure of where Michael is. At the Doyle house, when Laurie still receives no word from anyone, she grabs her keys and curiously ventures across the street. Upon reaching the front door, she finds it locked and rings the doorbell. There is no answer. Laurie walks around the side of the house to the kitchen door. Going inside, she searches around for any signs of Annie, Lynda, or Bob, thinking this is a trick. Not finding them anywhere, she walks upstairs and sees the light from a jack-o-lantern streaming underneath the bedroom door. Opening it, she sees in horror Annie's lifeless body on the bed with Judith Myers's headstone above her. In tears, Laurie backs against the closet when suddenly, Bob's body drops down into the doorway, hanging from the ceiling. Laurie screams in terror just as the closet door opens, revealing Lynda's body as well. Laurie runs out of the bedroom into the hallway, backing against the wall. Instantly, Michael's mask appears in the doorway behind her. Laurie walks forward, standing against the balcony, when Michael reaches out with his knife and stabs her in the shoulder! Laurie screams louder than ever and falls over the balcony railing, crashing down onto the staircase. Michael rushes over to the top of the stairs and begins walking toward her. Laurie leaps up and rushes towards the front door hurriedly, but it won't budge. She runs through the living room to the kitchen, locking the door behind her. She rushes to the kitchen door, the way she came in, but a rake has been shoved under the doorknob outside. She is trapped! Suddenly, Michael's hand breaks through the other door behind her as he turns the lock and enters the room. Terrified, Laurie smashes through the glass with her bare hand and knocks the rake over. Shoving the door open, she runs out of the house and stumbles into the yard. She screams for help and runs onto the porch of another house, but no one will help her. Hurrying across the street to the Doyle house, she reaches for the keys in her pocket, but they are gone! Panicking, she bangs on the door, but Tommy is fast asleep. Just then, Michael appears behind the Wallace house and Laurie begins to yell for Tommy. Grabbing a potted plant, she throws it at Tommy's bedroom window, waking him. He slowly walks downstairs, unaware of the trouble. Finally, he reaches the front door just in time and lets Laurie in. She locks the door and orders Tommy to go upstairs. Turning out the lights, Laurie believes that she is safe, when instantly, she sees in terror that a window is open. Scared beyond imagination, she crouches down in front of the couch when suddenly, Michael leaps out from behind the couch and tries to stab her, but he misses and hits the couch instead. Laurie grabs a knitting needle and swirls around, stabbing Michael in the neck. He staggers backward and hits the floor, apparently dead. Laurie, nearly passing out because of blood loss, drops the knife that is still in the couch onto the floor and goes upstairs to check on the kids.
Outside, Dr. Loomis still walks down the sidewalk when Mr. Brackett's police car pulls up. Dr. Loomis tells him that he found the Smith's Grove Sanitarium car and he will head over to where Michael is. Mr. Brackett drives away, now truly believing what is going on.
Upstairs at the Doyle house, Tommy and Lindsey run up to Laurie, thinking that it was the boogeyman who attacked her. She assures them that he is dead, but Tommy says that she couldn't have killed him because he is incapable of being harmed. At this moment, Michael lumbers toward them, and Tommy and Lindsey run back into the bedroom. Laurie scurries into another room, opening a set of doors leading to the balcony and, hiding in a closet, tries to fool Michael as to where she actually is. She ties a pair of stockings over the closet's doorknobs, but Michael soon begins shaking the doors and reaches through them with his knife, slicing the stockings! He breaks down the top half of the closet door and reaches in for Laurie, accidentally turning the light on. Laurie grabs a hanger and stabs Michael in the eye with its point. He jumps back in pain, dropping the knife into the closet. Laurie takes it, clutching it in her hands, and stabs Michael in the chest. He falls to the ground, dead. Laurie carefully slips out of the closet and, seeing this, drops the knife. Asking Tommy and Lindsey to come out, she tells them to go down the street to the McKenzies' house and tell them to call the police. They leave the house, screaming, attracting the attention of Dr. Loomis, who is outside and runs up to the Doyle house.
Inside, Laurie is slumping against the doorway of the room where she was hiding, tired and almost unconscious. She doesn't notice that Michael, thought to be dead, is slowly rising behind her. Laurie stands up, leaving the room, when suddenly, Michael grabs her by the neck and begins to strangle her. Laurie fights back and pulls his mask off, revealing Michael's true face. Instantly, Dr. Loomis appears at the top of the staircase and shoots Michael with his gun. Michael falls backwards into another room as Laurie falls against the wall behind her, covering her ears. Dr. Loomis chases the murderer into the other room and sees him standing in front of the balcony doors. Dr. Loomis shoots him five more times, causing him to fall out the doors and off the balcony. Michael slams onto the ground below, appearing to be dead. The doctor looks back at Laurie, who says, "...was the boogeyman." Dr. Loomis solemnly replies, "As a matter of fact, it was." Looking back down below, he sees in horror that Michael has vanished, but Dr. Loomis knew all along that this would happen. Laurie realizes that Michael still is not dead and begins sobbing. The film ends with a shot of the Myers' house and the sound of Michael breathing heavily behind his mask.
Michael Myers, the legendary man who came home on Halloween night to kill, is still alive somewhere out there...