A serial killer escapes from the asylum and returns to the town where he grew up.
In Haddonfield, Illinois, on Halloween night in 1963, Michael comes home and watches as Judith Myers and her Boyfriend start kissing. The Boyfriend asks if they are alone and Judith tells him that Micheal is around somewhere. Judith and her Boyfriend go upstairs and Michael walks into the house and grabs a knife from the kitchen. Judith and her Boyfriend finish having sex and her Boyfriend leaves. Michael then walks up the stairs to Judith's bedroom and stabs her to death. He walks out of the house and Michael's father finds Michael holding the large knife.
In Smith's Grove, Illinois, on October 30, 1978, Loomis is driving with Marion to the Illinois State Hospital. She tells him that the only thing that bothers her is when the mentally ill speak in gibberish. Loomis tells her that Michael hasn't spoken a word in fifteen years. He warns her not to underestimate Michael and that he never wants Michael to get out of the mental ward. Marion notices that some of the mental patients are just wandering around and Loomis tells her to hurriedly drive to the main gate. He gets out of the car and runs to the gate and Michael jumps onto the car and attacks Marion who manages to get out of the car. Michael then climbs into the car and drives away.
In Haddonfield on Halloween, Laurie leaves her house and as she is walking away, Laurie's Father asks her to drop off a key at the Myers house. Tommy runs up to Laurie and asks her if she is coming over that night. They walk to the Myers house and Tommy calls the house the spook house. Laurie puts the key under the door mat and as she walks away, Michael watches her. Tommy tells Laurie that Lonnie told him something bad happened at the Myers house. Dr. Wynn tells Loomis that he isn't responsible for Michael's escape and blames Loomis for not telling the authorities how dangerous Michael was. During class, Laurie looks outside the classroom window and sees a state of Illinois vehicle parked outside. At Tommy's school, Lonnie, Richie and Keith pick on Tommy and his giant pumpkin he is carrying around. They tease him that the boogeyman is going to get him and the trip him and run away. As he is running away, Richie almost runs into Michael and Michael starts following Tommy. Loomis uses a payphone to call the police department in Haddonfield and warns them that Michael is on his way there. He notices an abandoned truck and finds the matchbook that Marion had in the car. Lynda makes fun of Laurie for all the books she is carrying around and complains about everything she has to get done.
Annie catches up to them and tells them that Paul was grounded by his parents and can't come over. As they are talking they see Michael drive past them. Annie yells at Michael and he stops the car and then eventually continues on his way. Lynda asks Annie if her and Bob can still come over and Annie tells her that the Wallace's leave at 7. As Laurie and Annie are walking Laurie sees Michael staring at them, but he then disappears. Laurie walks into Brackett and he tells her that on Halloween everyone is entitled to one good scare. Laurie goes to her room and looks out her window and sees Michael staring at her, but then disappear again. Later, Annie picks Laurie up. Loomis goes to the cemetery and the Graveyard Keeper takes him to Judith's grave and they find the headstone missing. Laurie and Annie smoke a joint and Laurie tells Annie about seeing Michael staring up at her. As they drive by Nichols Hardware, they see Brackett. They stop and Brackett tells them that somebody broke into the hardware store and took some masks, rope and a couple of knives. Loomis drives up to Brackett and tells him that he needs to speak to him. Laurie tells Annie that she wants to go out with Ben Tramer and as they are driving, Michael is following behind them.
Annie goes to Lindsey's house to babysit her and Michael watches Lindsey's parents leave. Loomis and Brackett drive to the Myers house and they find a partially eaten dog inside and Loomis tells Brackett of when he first met Michael who he describes as emotionless and pure evil. Annie calls Laurie and Lester starts barking. Annie tells Laurie that she told Ben Tramer that Laurie liked him and Tommy sees Michael staring towards the house. Annie spills something on her shirt and hangs up the phone. Lester starts barking at Michael and Michael kills him. Tommy and Laurie start watching The Thing from Another World (1951) and Tommy tells Laurie that he saw the boogeyman and Richie told him the boogeyman was going to get him. Annie goes to wash her clothes and gets stuck when the door won't open in the laundry room. Paul calls and asks Lindsey to tell Annie that he called. Lindsey goes to the laundry room and helps Annie. Annie talks to Paul and he tells her that his parents are gone and asks her to pick him up. Annie tells Lindsey she is going to bring her to watch television with Tommy and she drops Lindsey off with Laurie. As Annie gets inside her car to pick up Paul, Michael strangles her and then slashes her throat.
Tommy and Lindsey next watch Forbidden Plant (1956) and as Tommy is trying to scare Lindsey, he sees Michael carrying the body of Annie. He yells about seeing the boogeyman, but when Laurie looks, Michael is gone. Richie and Keith dare Lonnie to go inside the Myers house and Loomis scares them away. Brackett walks up to Loomis and tells him that he thinks Loomis is wrong about Michael coming into town. Lynda and Bob drive up to Lindsey's house in Bob's van and they go inside. They find the house empty and as they start kissing, Michael watches them from inside the house. Lynda calls Laurie and asks her where Annie is and Laurie tells her that Annie went to pick up Paul. Lynda and Bob have sex and Bob goes to the kitchen to get them a beer. He notices the back door is open and is then stabbed to death by Michael. Michael goes up to the bedroom wearing a sheet and Bob's glasses and Lynda thinks he is Bob. Lynda calls Laurie and as she is talking to her, Michael starts strangling Lynda and Laurie thinks Lynda is making pleasurable noises. Loomis notices the Illinois state vehicle parked nearby and starts walking towards the car. Laurie goes outside and goes to Lindsey's house. She goes inside and finds Annie's body on the bed with Judith's headstone nearby. Bob's body falls from the top of the hallway and Laurie finds Lynda's body in the closet.
Michael slashes Laurie in the arm, but she manages to get out of the house. She yells for help and knocks for help at a house nearby, but the people inside ignore her and turn off their lights. She gets back to Tommy's house and tells Tommy to run upstairs and lock the door. Laurie notices the back door is open and stabs Michael in the face with her knitting needles when he attacks her and Michael collapses to the ground. Brackett finds Loomis walking down the straight and Loomis tells him that Michael is nearby. Laurie goes to the room and tells Tommy and Lindsey that she killed Michael, but he appears behind her. Laurie tells Tommy and Lindsey to go into the bathroom and lock the door and she opens the window and then hides in the closet. Michael breaks the closet door and Laurie stabs him in the face with a wire hanger. He drops his knife and Laurie stabs him with it. She goes to the bathroom and tells Tommy and Lindsey to run out the house and go to the Mackenzie house. Loomis sees Tommy and Lindsey running and screaming and goes inside Tommy's house. Michael attacks Laurie again and Loomis shoots Michael numerous times until Michael falls out of the window. Laurie tells Loomis that Michael was the boogeyman and Loomis tells her it was. Loomis then looks out the window and Michael's body is gone.