Single woman Lavinia Nibbs is sitting at home on her porch, pouring herself a glass of lemonade. Her friend Francine arrives to leave with her on their date and Lavinia locks up the house, setting down her glass of lemonade before she can drink it. As Lavinia prepares to leave, Francine wonders if her older friend gets lonely living by herself, but Lavinia insists that she's fine. As the two friends walk down the street to a movie, their elderly neighbors tell them that they shouldn't go out while the Lonely One, a serial killer, is on the loose. The two friends discuss the killer and Francine worries that he'll find them. As they walk by the woods, Lavinia daringly suggest that they cut through the ravine and take a shortcut to the theater and convinces Francine to go with her. As they walk through the ravine, Lavinia talks about the Boogeyman and describes how in the stories, he walks up the stairs in the house of his victims, one step at a time. The women come to a halt when they find a corpse: their friend Elizabeth, strangled.
Officer Kennedy arrives to conduct the investigation while his men secure the crime scene. He tells the two women to go home but Lavinia insists on going to the show with their third friend, Helen, and not letting the Lonely One ruin their night out. As they leave the ravine, Francine spots some curious boys watching them and yells at them to go home.
At Helen's house, Lavinia and Francine just tell their friend that someone found Elizabeth's body, but avoid telling her they were the ones who found it. Helen insists on staying home but Lavinia tells her two friends that she's going to the theater. Francine and Helen reluctantly go with her and Lavinia assures them that the Lonely One only attacks once a month so now they're safe. A man suddenly leaps out at them but they realize it's Frank Dillon, a local man. Francine screams in terror and Frank apologizes, and the other two women tell him off.
The trio stops at the drugstore for candy and the druggist tells them that a man in a black suit with a pale face was asking after Lavinia. The druggist admits that he told the man the street where she lives. As the women leaves, Lavinia admits that it might be exciting if he was the Lonely One, and her two friends wonder about her. Frances admits that Lavinia is the prettiest woman in town, now that Elizabeth is dead, and can't understand why she didn't get married years ago. When Helen and Francine hesitate, Lavinia insists on going to the theater and tells them she'll go by herself if she has to, but she is going. Helen and Francine accompany her to the movie. Before the feature starts, the theater manager tells them that they're going to skip the shorts so everyone can be done early and then go home immediately afterward. The movie, a thriller, plays on the screen. A pale man in a black suit sits behind the women and Francine finally panics, screams that he's the Lonely One, and runs out to the lobby.
Later, the women go to the drugstore for sodas and discuss the fact that the man was the manager's brother. Lavinia figures that the Lonely One is long gone. The druggist closes up for the night and the trio walks home. Francine suggests they walk Lavinia home but Lavinia notes that then Francine would have to walk home. Instead, Francine suggests that they all stay at Lavinia's house overnight, and they start merrily singing as they go down the street. However, they notice a man watching them from his porch and abruptly stop.
When the women arrive at Francine's house, she asks the other two to stay. Lavinia refuses and says that she'll call her friend when she gets home safely. When Francine worries, Lavinia assures her that she'll live forever and has nothing to fear, and hugs her friend goodbye. As Lavinia and Helen pass the ravine, Lavinia says that she's going to take the shortcut instead. Helen wonders if she wants to die but Lavinia insists, and Helen leaves her and goes home by the street.
In the ravine, Lavinia takes the path but hears a man whistling the song they were singing earlier. She hides in the brush and sees a man approaching her, and then realizes it's Officer Kennedy. He offers to walk her home but Lavinia half-seriously accuses him of being the Lonely One and says that she'll walk home without him. Kennedy says he'll wait to make sure she gets across the ravine okay, but when Lavinia turns back a few steps later, she discovers that he's disappeared.
As Lavinia walks up the stairs on the other side of the ravine, she starts counting her steps and remembers her story about the Boogeyman. She thinks she hears someone behind her, and she runs into a branch, Panicking, Lavinia runs through the woods and trips at the spot where Elizabeth died. Staggering to her feet, Lavinia hears someone coming up behind her. She manages to crawl out of the ravine to the street and runs to her house, going inside and locking the door behind her.
Lavinia finally manages to get control of herself and starts to call Francine. She tells her friend that she made it home safely and hangs up. She looks out on the porch and notices the glass of lemonade. However, it's now empty. Turning, Lavinia realizes that the Lonely One has been sitting in her chair and waiting for her the entire time.