Gourmet writer Justus Walters is in his apartment working on his latest manuscript when the phone rings. He picks it up and tells the woman at the other end, Elizabeth Croft, that he doesn't want her to call. Justus hangs up and then listens to footsteps coming down from above. The doorbell rings and he yells at Elizabeth that he doesn't want to be disturbed. He finally goes to the door and she begs him to talk to her. Justus says that she's obsessed with 19th century novels and tells her that he has no interest in continuing a relationship with her. He only took her out to dinner once to be neighborly, but he's had enough and slams the door in her face. Elizabeth says one last thing through the door, that someday she hopes he'll need someone when he's helpless. She walks away, and then screams. Justus looks out and sees her on the steps. She claims to have tripped and needs help, but he immediately realizes that she's faking and closes the door again.
When he hears the faucet dripping, Justus goes to his kitchen and discovers a spider in the sink. He washes it down the drain and goes back to his desk, but hears the faucet dripping again. He goes back out and shuts off the faucet, and sees the spider in the sink again. When he gets a towel to smash it, Justus discovers that it has grown larger. He washes it down the drain again, and the doorbell rings. It's the building janitor, Boucher, who is there to fix the thermostat. Justus complains about the spider. Boucher is less than sympathetic, even with Justus explains he has a phobia about spiders. The janitor refuses to call an exterminator and tells Justus he needs to man up. Once he's done with the thermostat, Boucher walks out on the disgusted writer.
Justus glances at the sink, but hears something squeaking in his bedroom. He opens the door and finds the spider, now several three feet long. The writer slams the door on it and goes to get Boucher. The janitor figures that Justus is drunk and goes back to bed. The writer finally goes upstairs to Elizabeth's apartment and knocks, and she asks what he wants. He suggests she invite him in for a brandy, and she reluctantly agrees. Once inside, Elizabeth suggests that he apologize, and Justus does so, awkwardly. She realizes that he's shaking but he lies and says that he likes her. She doesn't believe it, and Justus admits that he's afraid of spiders and there is a giant one in his apartment. Elizabeth laughs and says she's never read any literature about spiders that large, and Justus suggests it might be a mutation. He uses her phone to call the police, but she interrupts to suggest he call a room at the psychiatric hospital. Elizabeth warns that they'll lock him away, and that he's the only one who can see the spider. She suggests that he might be drinking, and tells him to get out. As Justus goes, he asks her to come with him and she agrees to take a chance.
Justus and Elizabeth go downstairs to his apartment and he hesitates, but Elizabeth goes inside, unconcerned. There's no sign of the spider in the living room and kitchen, and he suggests she check the bedroom. Elizabeth opens the door and finds nothing, and tells him it's empty just like his life. She takes his hand and ushers him inside, and then closes and locks the door behind him, giggling. Justus begs her to let him out, and she says she'll come down in the morning. A squealing noise fills the room and Justus backs up in horror, while Elizabeth walks away.