On Halloween night, 1963, in Haddonfield, Illinois, six-year-old Michael Myers stabs his teen sister, Judith, to death with an over-sized butcher's knife just after she has sex with her boyfriend. On 30 October 1978, in Smith's Grove, Illinois, Michael's long-time psychiatrist, Dr. Sam Loomis, and an accompanying nurse drive to the maximum-security sanitarium where Michael, now twenty-three years old, is committed. Although they must, in accordance with the law, take Michael to court for a judge to evaluate his mental state, Loomis believes Michael is pure evil and admits he hopes "it" never gets out. As the car approaches the sanitarium grounds, Loomis and the nurse realize something is wrong: the patients are loose. When Loomis gets out of the car to open the front gate, Michael shatters the car window and takes off in the vehicle. On Halloween day, Haddonfield teen Laurie Strode heads off to school. She drops off a key at the vacant Myers house at the request of her realtor father and in spite of warnings from Tommy Doyle, the young boy Laurie frequently babysits, that the house is haunted. Laurie is unaware that Michael is inside, watching her. Later, in class, she spots Michael watching her from the street outside. This continues throughout the day, as he trails her and her friends around town, always vanishing quickly after he is spotted. When the elementary school lets out, three boys taunt little Tommy, teasing him that the Boogeyman is coming for him that night. As the boys chant this, an unnoticed Michael lingers in the distance, watching Tommy as he leaves for home. Back in Smith's Grove, Loomis, unconvinced that the sanitarium officials understand the threat Michael poses, sets out to recapture him personally. Guessing that Michael will go to Haddonfield, Loomis phones the Haddonfield police to warn of Michael's homecoming. On his way to Haddonfield, Loomis discovers an abandoned pickup truck containing Michael's discarded patient's robes and the "Rabbit in Red" matchbook the nurse was using the night before. He does not, however, notice the stripped body of the driver discarded in the brush. Later that afternoon, Laurie and her friend, Annie Brackett, carpool to their babysitting jobs. Laurie is watching Tommy for the night, while Annie is babysitting his neighbor Lindsey Wallace. En route, the two smoke a joint and chat casually about boys, unaware that Michael is trailing them in the stolen station wagon. They run into Annie's father, Sheriff Brackett, who is responding to a robbery at a hardware store. He tells the girls that children were responsible for the break-in, because only a Halloween mask, rope, and knives were stolen. Loomis, having just discovered that Judith Myers's tombstone is missing, arrives at the scene to ask the sheriff for his assistance in apprehending Michael. As the girls drive off, Loomis does not notice his stolen car pulling away in pursuit. It is night by the time Laurie and Annie arrive at their destinations. The trailing Michael parks and watches each girl but ultimately follows Annie. Loomis and Brackett visit the Myers house in search of clues. Inside it they find the fresh carcass of a slaughtered dog, proof for Loomis that Michael is near. Upstairs, in Judith's former bedroom Loomis recounts her murder. However, he is interrupted when a rain gutter crashes through a nearby window. Startled, Loomis draws a concealed pistol. He admits to Brackett that he is scared, and recalls his first meeting with Michael fifteen years before, describing the boy as empty, devoid of reason, conscience, or understanding, a six-year-old with "the blackest eyes, the devil's eyes." Truly, he believes Michael is evil. Across the street from one another Laurie and Annie talk on the phone, while Michael, donning a ghostly white mask, creeps outside the Wallace house. Though Lester, the Wallace's family dog, senses Michael's presence, Annie, annoyed at the dog's barking, fails to heed his warning. Eventually Michael crushes the dog, permanently silencing the pet. From his house, Tommy spots Michael and runs to tell Laurie that the Boogeyman is outside, but Michael has vanished by the time she looks. When Tommy again mentions his concern about the Boogeyman, Laurie consoles the child, by promising that she will protect him. At Lindsey's house, Michael watches as Annie spills butter on herself and goes to the outside laundry room to wash her clothes. While in the laundry room, Annie is accidentally locked in, and, though danger looms just outside, she is unaware and more concerned with an expected phone call from her boyfriend, Paul. When Paul finally calls, Annie is stuck in the laundry room's obstructed window, after she unsuccessfully attempts to squeeze through it. With Lindsey's help, Annie eventually works her way free and arranges a night of sexual escapades with Paul. Annie then convinces Laurie to watch Lindsey, so she can pick up Paul. However, Michael chokes Annie and eventually slits her throat in her car before she can leave. Tommy sees Michael once again, this time carrying Annie's corpse into Lindsey's house. Again, he screams out to Laurie that the Boogeyman is outside, but, as before, she does not believe him. Laurie's friend, Lynda, and her boyfriend, Bob, arrive drunk at the Wallace house intent on using it as a love nest. Finding no one home, the two make out on the couch while an unseen Michael watches from the hallway. Upon learning from Laurie that Lindsey is out for the night, Lynda and Bob move their escapades upstairs. After they have sex, Bob leaves Lynda to retrieve beers from the downstairs fridge. Michael kills Bob in the kitchen, pinning him to the wall with a knife. Then Michael dons a sheet and Bob's glasses and returns to Lynda. When Lynda quickly becomes annoyed at "Bob's" silence, she calls Laurie. However, before she can speak, Michael strangles Lynda with the telephone cord. Laurie hears only "squealing" on the end of the line and assumes Annie is playing a prank, though she becomes increasingly concerned. Noticing lights on at Lindsey's house, Laurie heads over to see if Annie is okay. Meanwhile, Dr. Loomis, having spent the night casing the Myers house, discovers his stolen car down the street. Lindsey's house is dark when Laurie arrives, except for the upstairs bedroom that is illuminated by a jack-o-lantern. When Laurie opens the bedroom door, she discovers Lynda's corpse arranged on the bed, below Judith Myers's stolen tombstone. Terrified, Laurie cowers back, into the closet, where Bob's corpse swings down onto her. She screams and retreats to another part of the room where she discovers Annie bloodied and dead. Laurie stumbles out of the room and into the hallway where a waiting Michael slashes her in the arm with a knife. The shock sends Laurie over the banister and onto the stairs below. Injured, but mobile, she escapes out the back door, screaming out for help. She retreats to Tommy's house pursued by Michael. Once inside, she locks the door and tells Tommy to lock Lindsey and himself upstairs. In the house, Laurie finds the phone line dead and a window ajar. She cowers by the couch clutching a large knitting needle for protection. With knife in hand, Michael rears from behind the couch, but the desperate Laurie stabs him in the neck with the needle. Michael lays limp on the floor as Laurie grips his dropped knife. Outside, Loomis, having informed Brackett about the finding of his car, scours the neighborhood for any sign of Michael. Convinced that she has disabled Michael, Laurie retrieves Tommy and Lindsey, but before they can leave the house Michael rises. Spotting Michael ascending the stairs, Laurie locks the children in an upstairs bathroom while she escapes into a bedroom closet. Inside the closet, she rigs its doors shut, forcing Michael to break through it. As he smashes his way into to the closet, Laurie fashions a clothes hanger into a weapon and jabs Michael through the eye. Injured, Michael again drops the knife, which Laurie uses to stab him. Once more Michael crumbles to the floor motionless. Laurie leaves the closet, drops the knife, and gathers the children, whom she sends across the street for help. A wounded Laurie shrinks to the floor with her back to Michael. Silently, Michael sits up, and, as Laurie stands to leave, he again lunges at her. The two struggle briefly in the hallway before Loomis rushes up the stairs and shoots Michael. The force of the bullets sends Michael crashing through the upstairs window, falling to the lawn below where he lays lifeless. A tearful Laurie declares that Michael is the Boogeyman, and Loomis agrees. Still wary, Loomis surveys the lawn for Michael's body, but it is gone.